1-9 A-D E-G H-M N-P Q-S T-Z


CAS NO: 56-40-6
Synonyms: Aminoacetic acid; Amino acetic acid; acid; amino; acetic; 2-Aminoethanoic acid; Glycocoll; glycol; glikol; glukol; glucol; glycine; 2-Aminoacetic acid; 56-40-6; aminoacetic acid; Glycocoll; Aminoethanoic acid; Glycolixir; Glycosthene; Aciport; Glicoamin; Glycin; H-Gly-OH; Padil; L-Glycine; Hampshire glycine; Leimzucker; Amitone; Acetic acid, amino-; Aminoazijnzuur; Glycine, non-medical; Sucre de gelatine; Gyn-hydralin; GLY (IUPAC abbrev); Glycinum; Corilin; Glyzin; Glycinum [INN-Latin]; Glicina [INN-Spanish; Glycine [INN]; Glykokoll; gly; Acide aminoacetique [INN-French]; Acido aminoacetico [INN-Spanish]; Acidum aminoaceticum [INN-Latin]; FEMA No. 3287; CCRIS 5915; HSDB 495; glycyl radical; AI3-04085; amino-Acetic acid; UNII-TE7660XO1C; NSC 25936; [14C]glycine; GLYCINE 1.5% IN PLASTIC CONTAINER; EINECS 200-272-2; MFCD00008131; CHEMBL773; AMINOACETIC ACID 1.5% IN PLASTIC CONTAINER; Glycine iron sulphate (1:1); TE7660XO1C; CHEBI:15428; 2-aminoaceticacid; DHMQDGOQFOQNFH-UHFFFAOYSA-N; aminoacetate; NSC25936; Athenon; polyglycine; NCGC00024503-01; Glicina; DSSTox_CID_667; Glycine, free base; Polyglycine II; Acido aminoacetico; Acide aminoacetique; DSSTox_RID_75720; DSSTox_GSID_20667; 25718-94-9; Acidum aminoaceticum; Glycine, 99%, ACS reagent; Glycine, 99+%, for analysis; Aminoessigsaeure; Hgly; CAS-56-40-6; Glycine, labeled with carbon-14; Glycine [USP:INN]; H2N-CH2-COOH; Glycine, homopolymer (VAN); Aminoessigsaure; Aminoethanoate; 18875-39-3; amino-Acetate; 2-aminoacetate; Glycine;; glycine USP; Glycine Technical; glycine-13c; [3H]glycine; Glycine, EP/USP; H-Gly; L-Gly; Gly-CO; Gly-OH; L-Glycine,(S); [14C]-glycine; Corilin (Salt/Mix); Glycine 1 M solution; PubChem18924; Tocris-0219; Glycine (H-Gly-OH); NH2CH2COOH; Glycine, >=99%; 13479-54-4; 13682-92-3; Aminoacetic acid,medicinal; Glycine (JP17/USP); Glycine, 99%, FCC; Biomol-NT_000195; bmse000089; bmse000977; WLN: Z1VQ; EC 200-272-2; Gly-253; GTPL727; AB-131/40217813; KSC205S9D; BPBio1_001222; GTPL4084; GTPL4635; DTXSID9020667; BDBM18133; Buffer Concentrate, pH 11.01; CTK1A5991; Glycine, >=99.0% (NT); Glycine, 98.5-101.5%; Pharmakon1600-01300021; BCP25965; CS-B1641; HY-Y0966; KS-000002MW; ZINC4658552; Glycine, ACS reagent, >=98.5%; Tox21_113575; ANW-32505; Glycine, 99%, natural, FCC, FG; LS-218; NSC-25936; NSC760120; STL194276; Glycine, purum, >=98.5% (NT); Glycine, tested according to Ph.Eur.; AKOS000119626; Glycine, for electrophoresis, >=99%; Tox21_113575_1; AM81781; DB00145; MCULE-2415764032; NSC-760120; RTC-066530; Glycine, BioUltra, >=99.0% (NT); Glycine, BioXtra, >=99% (titration); Glycine, SAJ special grade, >=99.0%; NCGC00024503-02; NCGC00024503-03; AK-77854; BP-31024; BR-77854; Glycine, Vetec(TM) reagent grade, 98%; SC-26884; AB1002628; DB-029870; ST2416448; TC-066530; FT-0083159; FT-0600491; G0099; G0317; Glycine, ReagentPlus(R), >=99% (HPLC); A20662; Aminoacetic acid; Aminoethanoic acid; Glycocoll; C00037; D00011; M-6155; M03001; L001246; Q620730; SR-01000597729; Glycine, certified reference material, TraceCERT(R); Q-201300; SR-01000597729-1; Q27115084; B72BA06C-60E9-4A83-A24A-A2D7F465BB65; F2191-0197; Glycine, European Pharmacopoeia (EP) Reference Standard; Z955123660; Glycine, BioUltra, for molecular biology, >=99.0% (NT); InChI=1/C2H5NO2/c3-1-2(4)5/h1,3H2,(H,4,5; UNII-0O72R8RF8A component DHMQDGOQFOQNFH-UHFFFAOYSA-N; Glycine, United States Pharmacopeia (USP) Reference Standard; Glycine, Pharmaceutical Secondary Standard; Certified Reference Material; Tris-tricine buffer; Tris-glycine buffer;Tris glycine buffer concentrate; Glycine, analytical standard, for nitrogen determination according to Kjeldahl method; Glycine, from non-animal source, meets EP, JP, USP testing specifications, suitable for cell culture, >=98.5%; Glycine, meets analytical specification of Ph. Eur., BP, USP, 99-101% (based on anhydrous substance); Glycine, PharmaGrade, Ajinomoto, EP, JP, USP, manufactured under appropriate GMP controls for Pharma or Biopharmaceutical production, suitable for cell culture; Glycine, puriss. p.a., Reag. Ph. Eur., buffer substance, 99.7-101% (calc. to the dried substance); Acid, Aminoacetic; Aminoacetic Acid; Calcium Salt Glycine; Cobalt Salt Glycine; Copper Salt Glycine; Glycine; Glycine Carbonate (1:1), Monosodium Salt; Glycine Carbonate (2:1), Monolithium Salt; Glycine Carbonate (2:1), Monopotassium Salt; Glycine Carbonate (2:1), Monosodium Salt; Glycine Hydrochloride; Glycine Hydrochloride (2:1); Glycine Phosphate; Glycine Phosphate (1:1); Glycine Sulfate (3:1); Glycine, Calcium Salt; Glycine, Calcium Salt (2:1); Glycine, Cobalt Salt; Glycine, Copper Salt; Glycine, Monoammonium Salt; Glycine, Monopotassium Salt; Glycine, Monosodium Salt; Glycine, Sodium Hydrogen Carbonate; Hydrochloride, Glycine; Monoammonium Salt Glycine; Monopotassium Salt Glycine; Monosodium Salt Glycine; Phosphate, Glycine; Salt Glycine, Monoammonium; Salt Glycine, Monopotassium; Salt Glycine, Monosodium; Acide Aminoacétique; Acide Amino-Acétique; Aminoacetic Acid; Atheno; Free Base Glycine; G Salt; Glicina; Glycine de Base Libre; Glycocoll; Glycosthene; Iconyl; L-Glycine; Monazol; GLYCINE; GLİSİN; GLYSİN; AMİNO ASİT; AMINO ACID; AMINOALKOLIC ACID; AMİNO ALKALİK ASİT;SOJA; SOYA; SOY BEAN; SOJA BEAN; GLYCINE MAX; GENUS GLYCINE; FENUSA; FAMILY TENTHREEDINIDAE; ARTHROPOD GENUS; 2-AMINOACETIC ACID; ACETIC ACID,AMINO-; ACIDE AMINOACETIQUE; ACIDO AMINOACETIO; AMINO-ACETIC ACID; AMINOACETIC ACID; AMINOETHANOIC ACID; GLICINA; GLY; GLYCIN; GLYCINE ZWITTERION; GLYCOCOLL; H2N-CH2-COOH; LEIMZUCKER; 2-AMINOACETICACID; 2-AMINOETHANOIC ACID; 2-AZANYLACETIC ACID; ACIDUM AMINOACETICUM; ACIPORT; AMINO(CARBOXY)METHYL; AMINO-ACETICACID; AMINOAZIJNZUUR; AMINOESSIGSAEURE;AMITONE;CORILIN; GLICOAMIN; GLU; GLYCINE; WISTERIA; GLYCINE-RICH; GENUS GLYSINE; CHELATED; GLYCINE RESIDUE; TRIMETHYLGLYCINE; WISTARIA; YOSHİFUJİ; FUJİ; LANE; TONAİ; JAPANASE WİSTERİA GLYCINES; MILACEMIDE; CHOLYLGLYCINE; ALLYLGLYCINE;PENTAGLYCINE; GLYCINOL; GDA; GLYCINATE; GLYCINAL; GLYCINATE GLYCINASE; MONOSODIUM SALT; GLYSINE MONOPOTASSIUM SALT; KOBALT TUZU; SODYUM GLISIN; GLYZIN.


Top 9 Benefits and Uses of Glycine
Glycine is an amino acid that your body uses to create proteins, which it needs for the growth and maintenance of tissue and for making important substances, such as hormones and enzymes.

Your body naturally produces glycine from other amino acids, but it's also found in protein-rich foods and available as a dietary supplement.

Along with being a component of protein, glycine has several other impressive health benefits.

Here are the top 9 health benefits and uses of glycine.
1. Needed to Produce a Powerful Antioxidant
Glycine is one of three amino acids that your body uses to make glutathione, a powerful antioxidant that helps protect your cells against oxidative damage caused by free radicals, which are thought to underlie many diseases (1Trusted Source).

Without enough glycine, your body produces less glutathione, which could negatively affect how your body handles oxidative stress over time (2Trusted Source, 3Trusted Source).

In addition, because glutathione levels naturally decline with age, ensuring that you get enough glycine as you get older may benefit your health.
Glycine helps your body make glutathione, an important antioxidant that protects your body against cell damage.
2. A Component of Creatine
Glycine is also one of three amino acids that your body uses to make a compound called creatine.

Creatine provides your muscles with energy to perform quick, short bursts of activity, such as weightlifting and sprinting.

When combined with resistance training, supplementing with creatine has been shown to increase muscle size, strength and power (4Trusted Source, 5Trusted Source, 6Trusted Source).

It has also been studied for its beneficial effects on bone health, brain function and neurological conditions like Parkinson's and Alzheimer's disease (7Trusted Source, 8Trusted Source, 9Trusted Source).

While your body naturally creates creatine and it can be obtained through your diet, getting too little glycine may reduce how much you produce (10Trusted Source).

Glycine is a component of creatine, a compound that provides your muscles with energy and has been associated with other health benefits, such as improved bone health and brain function.

3. The Main Amino Acid in Collagen
Collagen is a structural protein that contains high amounts of glycine. In fact, every third to fourth amino acid in collagen is glycine (11Trusted Source).

Collagen is the most abundant protein in your body. It provides strength for your muscles, skin, cartilage, blood, bones and ligaments.

Supplementing with collagen has been shown to benefit skin health, relieve joint pain and prevent bone loss (12Trusted Source, 13Trusted Source, 14Trusted Source).

Therefore, it's important that you get enough glycine to support your body's production of collagen.

Glycine is the most abundant amino acid in collagen, a structural protein that has several health benefits, including for your skin, joints and bones.
4. May Improve Sleep Quality
Many people struggle to get a good night's rest, either because they have trouble falling or staying asleep.

While there are several ways you can improve your sleep quality, such as not drinking caffeinated beverages late in the day or avoiding bright screens a few hours before bedtime, glycine may also help.

This amino acid has a calming effect on your brain and could help you fall and stay asleep by lowering your core body temperature (15Trusted Source, 16Trusted Source).

Research in people with sleep issues has shown that taking 3 grams of glycine before bed decreases how long it takes to fall asleep, enhances sleep quality, lessens daytime sleepiness and improves cognition (17, 18).

For this reason, glycine may be a good alternative to prescription sleeping pills for improving sleep quality at night and tiredness during the day.

Glycine may promote sleep and enhance the quality of your sleep through its calming effects on the brain and its ability to lower core body temperature.
5. May Protect Your Liver From Alcohol-Induced Damage
Too much alcohol can have damaging effects on your body, especially your liver.

There are three primary types of alcohol-induced liver damage (19Trusted Source):

Fatty liver: A buildup of fat inside your liver, increasing its size.
Alcoholic hepatitis: Caused by inflammation of the liver resulting from long-term, excessive drinking.
Alcoholic cirrhosis: The final phase of alcoholic liver disease, occurring when the liver cells are damaged and replaced by scar tissue.
Interestingly, research suggests that glycine may reduce the harmful effects of alcohol on your liver by preventing inflammation.

It has been shown to reduce concentrations of alcohol in the blood of alcohol-fed rats by stimulating the metabolism of alcohol in the stomach rather than the liver, which prevented the development of fatty liver and alcoholic cirrhosis (20Trusted Source).

What's more, glycine may also help reverse liver damage caused by excessive alcohol intake in animals.

While moderate alcohol-induced liver damage can be reversed by abstaining from alcohol, glycine may improve the recovery process.

In a study in rats with alcohol-induced liver damage, the liver cell health returned to baseline 30% faster in a group fed a glycine-containing diet for two weeks compared to a control group (21Trusted Source).

Despite promising finds, studies on the effects of glycine on alcohol-induced liver damage are limited to animals and cannot be translated to humans (22Trusted Source, 23Trusted Source, 24Trusted Source).

Eating a diet with glycine decreases and reverses alcohol-induced liver injury in rats, but its effects in humans are unknown.
6. May Protect Your Heart
Increasing evidence suggests that glycine offers protection against heart disease.

It prevents the accumulation of a compound that, in high amounts, has been linked to atherosclerosis, the hardening and narrowing of the arteries (25Trusted Source, 26Trusted Source, 27Trusted Source, 28Trusted Source).

This amino acid may also improve your body's ability to use nitric oxide, an important molecule that increases blood flow and lowers blood pressure (29Trusted Source).

In an observational study in over 4,100 people with chest pains, higher levels of glycine were associated with a lower risk of heart disease and heart attacks at a 7.4-year follow-up (28Trusted Source).

After accounting for cholesterol-lowering medications, the researchers also observed a more favorable blood cholesterol profile in people who had higher glycine levels (28Trusted Source).

What's more, glycine has been found to reduce several risk factors of heart disease in rats fed a high-sugar diet (29Trusted Source).

Eating and drinking too much added sugar can raise blood pressure, increase levels of fat in your blood and promote dangerous fat gain around the belly - all of which can promote heart disease (30Trusted Source).

While encouraging, clinical studies on the effects of glycine on heart disease risk in humans are needed before it can be recommended (31Trusted Source).

Glycine may lower heart disease risk factors by preventing the build-up of a molecule associated with heart disease and by increasing your body's ability to use nitric oxide.
7. May Aid People With Type 2 Diabetes
Type 2 diabetes may lead to low levels of glycine.

It's a condition characterized by impaired insulin secretion and action, meaning your body doesn't produce enough insulin or that it doesn't respond properly to the insulin it makes (32Trusted Source).

Insulin decreases your blood sugar levels by signaling its uptake into cells for energy or storage.

Interestingly, because glycine has been shown to increase insulin response in people without diabetes, it's suggested that glycine supplements may improve impaired insulin response in people with type 2 diabetes (11Trusted Source, 33Trusted Source, 34Trusted Source).

Higher levels of glycine are associated with a reduced risk of type 2 diabetes, even after accounting for other factors that are associated with the condition, such as lifestyle (35Trusted Source, 36Trusted Source).

Therefore, people with type 2 diabetes may benefit from supplementing with glycine, though research is too preliminary to make any specific recommendations.

If you have type 2 diabetes, the best way to reduce your insulin resistance is through weight loss by means of diet and exercise (37Trusted Source).

Supplementing with glycine may improve impaired insulin action, a hallmark of type 2 diabetes. However, research to make any specific recommendations for its use in people with the condition is insufficient.
8. May Protect Against Muscle Loss
Glycine may reduce muscle wasting, a condition that occurs with aging, malnutrition and when your body is under stress, such as with cancer or severe burns.

Muscle wasting leads to a harmful reduction in muscle mass and strength, which declines functional status and can complicate other potentially present diseases (38Trusted Source).

The amino acid leucine has been studied as a treatment for muscle wasting, as it strongly inhibits muscle breakdown and enhances muscle building (39Trusted Source).

However, several changes in the body during muscle-wasting conditions impair the effectiveness of leucine for stimulating muscle growth.

Interestingly, in mice with muscle wasting conditions, such as cancer, research has shown that glycine was able to stimulate muscle growth whereas leucine was not (40Trusted Source, 41Trusted Source).

Therefore, glycine holds promise for improving health by protecting muscles from wasting during various wasting conditions (42Trusted Source).

Still, more research in humans is needed.

Glycine may preserve muscle mass in wasting conditions, such as cancer, malnutrition and burns, though more research in humans is needed.
9. Easy to Add to Your Diet
Glycine is found in varying amounts in meat, especially in tough cuts like the chuck, round and brisket.

You can also get glycine from gelatin, a substance made from collagen that's added to various food products to improve consistency.

Other and more practical ways to increase your intake of glycine include:

Add It to Foods and Drinks
Glycine is readily available as a dietary supplement in capsule or powder form. If you don't like taking pills, the powder form dissolves easily in water and has a sweet taste.

In fact, the name glycine is derived from the Greek word for "sweet."

Due to its sweet taste, you can easily incorporate glycine powder into your diet by adding it to:

Coffee and tea
Protein shakes
Take Collagen Supplements
Glycine is the main amino acid in collagen, the main structural protein of connective tissue, such as bone, skin, ligaments, tendons and cartilage.

Accordingly, you can boost your glycine intake by taking collagen protein supplements.

This is likely more efficient, as glycine competes with other amino acids for absorption and is therefore absorbed less efficiently by itself than when it's bound to other amino acids, as in the case of collagen (43Trusted Source, 44Trusted Source).

Is Glycine Safe?
Supplementing with glycine is safe in appropriate amounts.

Studies have used up to 90 grams of glycine per day over several weeks without serious side effects (45Trusted Source).

For comparison, the standard dose used in studies is about 3-5 grams per day.

Glycine powder is readily available and can easily be added to your favorite drinks and some foods. Collagen supplements are also an efficient way to boost your glycine intake. Both methods are a safe way to get more of this important nutrient.
The Bottom Line
Glycine is an amino acid with many impressive health benefits.

Your body needs glycine to make important compounds, such as glutathione, creatine and collagen.

This amino acid may also protect your liver from alcohol-induced damage and improve sleep quality and heart health.

What's more, glycine may also benefit people with type 2 diabetes and protect against muscle loss that occurs with muscle-wasting conditions.

You can increase your intake of this important nutrient by eating some meat products, by adding the powdered supplement form to drinks and foods or by supplementing with collagen.

From Wikipedia, the free encyclopedia
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For other uses, see Glycine (disambiguation).
"Gly" redirects here. For the unit of measurement, see light-year.
Glycin - Glycine.svg
Canonical amino acid form
Zwitterion of glycine
Zwitterionic form at physiological pH
Preferred IUPAC name
Aminoacetic acid
Systematic IUPAC name
2-Aminoethanoic acid
Other names
CAS Number
56-40-6 ☑
3D model (JSmol)
Interactive image
Zwitterion: Interactive image
Abbreviations Gly, G
CHEBI:15428 ☑
ChEMBL773 ☑
730 ☑
DB00145 ☑
ECHA InfoCard 100.000.248
EC Number
D00011 ☑
PubChem CID
TE7660XO1C ☑
CompTox Dashboard (EPA)
DTXSID9020667 Edit this at Wikidata
Chemical formula
Molar mass 75.067 g·mol-1
Appearance White solid
Density 1.1607 g/cm3[2]
Melting point 233 °C (451 °F; 506 K) (decomposition)
Solubility in water
24.99 g/100 mL (25 °C)[3]
Solubility soluble in pyridine
sparingly soluble in ethanol
insoluble in ether
Acidity (pKa) 2.34 (carboxyl), 9.6 (amino)[4]
Magnetic susceptibility (χ)
-40.3·10-6 cm3/mol
ATC code
B05CX03 (WHO)
Safety data sheet See: data page
Lethal dose or concentration (LD, LC):
LD50 (median dose)
2600 mg/kg (mouse, oral)
Supplementary data page
Structure and
Refractive index (n),
Dielectric constant (εr), etc.
Phase behaviour
Spectral data
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☑ verify (what is ☑☒ ?)
Infobox references
Glycine (symbol Gly or G;[5] /ˈɡlaɪsiːn/)[6] is an amino acid that has a single hydrogen atom as its side chain. It is the simplest amino acid (since carbamic acid is unstable), with the chemical formula NH2‐CH2‐COOH. Glycine is one of the proteinogenic amino acids. It is encoded by all the codons starting with GG (GGU, GGC, GGA, GGG). Glycine is integral to the formation of alpha-helices in secondary protein structure due to its compact form. For the same reason, it is the most abundant amino acid in collagen triple-helices. Glycine is also an inhibitory neurotransmitter - interference with its release within the spinal cord (such as during a Clostridium tetani infection) can cause spastic paralysis due to uninhibited muscle contraction.
Glycine is a colorless, sweet-tasting crystalline solid. It is the only achiral proteinogenic amino acid. It can fit into hydrophilic or hydrophobic environments, due to its minimal side chain of only one hydrogen atom. The acyl radical is glycyl.
History and etymology
Glycine was discovered in 1820 by the French chemist Henri Braconnot when he hydrolyzed gelatin by boiling it with sulfuric acid.[7] He originally called it "sugar of gelatin",[8][9] but the French chemist Jean-Baptiste Boussingault showed that it contained nitrogen.[10] The American scientist Eben Norton Horsford, then a student of the German chemist Justus von Liebig, proposed the name "glycocoll";[11][12] however, the Swedish chemist Berzelius suggested the simpler name "glycine".[13][14] The name comes from the Greek word γλυκύς "sweet tasting"[15] (which is also related to the prefixes glyco- and gluco-, as in glycoprotein and glucose). In 1858, the French chemist Auguste Cahours determined that glycine was an amine of acetic acid.[16]
Although glycine can be isolated from hydrolyzed protein, this is not used for industrial production, as it can be manufactured more conveniently by chemical synthesis.[17] The two main processes are amination of chloroacetic acid with ammonia, giving glycine and ammonium chloride,[18] and the Strecker amino acid synthesis,[19] which is the main synthetic method in the United States and Japan.[20] About 15 thousand tonnes are produced annually in this way.[21]

Glycine is also cogenerated as an impurity in the synthesis of EDTA, arising from reactions of the ammonia coproduct.[22]

Chemical reactions
Its acid-base properties are most important. In aqueous solution, glycine itself is amphoteric: at low pH the molecule can be protonated with a pKa of about 2.4 and at high pH it loses a proton with a pKa of about 9.6 (precise values of pKa depend on temperature and ionic strength).
Glycine functions as a bidentate ligand for many metal ions. A typical complex is Cu(glycinate)2, i.e. Cu(H2NCH2CO2)2, which exists both in cis and trans isomers.

As a bifunctional molecule, glycine reacts with many reagents. These can be classified into N-centered and carboxylate-center reactions.

The amine undergoes the expected reactions. With acid chlorides, one obtains the amidocarboxylic acid, such as hippuric acid[23] and acetylglycine.[24] With nitrous acid, one obtains glycolic acid (van Slyke determination). With methyl iodide, the amine becomes quaternized to give betaine, a natural product:
Glycine condenses with itself to give peptides, beginning with the formation of glycylglycine:

Pyrolysis of glycine or glycylglycine gives 2,5-diketopiperazine, the cyclic diamide.

Glycine is not essential to the human diet, as it is biosynthesized in the body from the amino acid serine, which is in turn derived from 3-phosphoglycerate, but the metabolic capacity for glycine biosynthesis does not satisfy the need for collagen synthesis.[25] In most organisms, the enzyme serine hydroxymethyltransferase catalyses this transformation via the cofactor pyridoxal phosphate:[26]

serine + tetrahydrofolate → glycine + N5,N10-Methylene tetrahydrofolate + H2O
In the liver of vertebrates, glycine synthesis is catalyzed by glycine synthase (also called glycine cleavage enzyme). This conversion is readily reversible:[26]

CO2 + NH+
4 + N5,N10-Methylene tetrahydrofolate + NADH + H+ ⇌ Glycine + tetrahydrofolate + NAD+
Glycine is degraded via three pathways. The predominant pathway in animals and plants is the reverse of the glycine synthase pathway mentioned above. In this context, the enzyme system involved is usually called the glycine cleavage system:[26]

Glycine + tetrahydrofolate + NAD+ ⇌ CO2 + NH+
4 + N5,N10-Methylene tetrahydrofolate + NADH + H+
In the second pathway, glycine is degraded in two steps. The first step is the reverse of glycine biosynthesis from serine with serine hydroxymethyl transferase. Serine is then converted to pyruvate by serine dehydratase.[26]

In the third pathway of its degradation, glycine is converted to glyoxylate by D-amino acid oxidase. Glyoxylate is then oxidized by hepatic lactate dehydrogenase to oxalate in an NAD+-dependent reaction.[26]

The half-life of glycine and its elimination from the body varies significantly based on dose.[27] In one study, the half-life varied between 0.5 and 4.0 hours.[27]

Glycine is extremely sensitive to antibiotics which target folate, and blood Glycine levels drop severely within a minute of antibiotic injections. Some antibiotics can deplete more than 90% of Glycine within a few minutes of being administered.[28]

Physiological function
The principal function of glycine is as a precursor to proteins. Most proteins incorporate only small quantities of glycine, a notable exception being collagen, which contains about 35% glycine due to its periodically repeated role in the formation of collagen's helix structure in conjunction with hydroxyproline.[26][29] In the genetic code, glycine is coded by all codons starting with GG, namely GGU, GGC, GGA and GGG.

As a biosynthetic intermediate
In higher eukaryotes, δ-aminolevulinic acid, the key precursor to porphyrins, is biosynthesized from glycine and succinyl-CoA by the enzyme ALA synthase. Glycine provides the central C2N subunit of all purines.[26]

As a neurotransmitter
Glycine is an inhibitory neurotransmitter in the central nervous system, especially in the spinal cord, brainstem, and retina. When glycine receptors are activated, chloride enters the neuron via ionotropic receptors, causing an inhibitory postsynaptic potential (IPSP). Strychnine is a strong antagonist at ionotropic glycine receptors, whereas bicuculline is a weak one. Glycine is a required co-agonist along with glutamate for NMDA receptors. In contrast to the inhibitory role of glycine in the spinal cord, this behaviour is facilitated at the (NMDA) glutamatergic receptors which are excitatory.[30] The LD50 of glycine is 7930 mg/kg in rats (oral),[31] and it usually causes death by hyperexcitability.

In the US, glycine is typically sold in two grades: United States Pharmacopeia ("USP"), and technical grade. USP grade sales account for approximately 80 to 85 percent of the U.S. market for glycine. If purity greater than the USP standard is needed, for example for intravenous injections, a more expensive pharmaceutical grade glycine can be used. Technical grade glycine, which may or may not meet USP grade standards, is sold at a lower price for use in industrial applications, e.g., as an agent in metal complexing and finishing.[32]

Animal and human foods

Structure of cis-Cu(glycinate)2(H2O).[33]
Glycine is not widely used in foods for its nutrional value, except in infusions. Instead glycine's role in food chemistry is as a flavorant. It is mildly sweet, and it counters the aftertaste of saccharine. It also has preservative properties, perhaps owing to its complexation to metal ions. Metal glycinate complexes, e.g. copper(II) glycinate are used as supplements for animal feeds.[21]

Chemical feedstock
Glycine is an intermediate in the synthesis of a variety of chemical products. It is used in the manufacture of the herbicides glyphosate,[34] iprodione, glyphosine, imiprothrin, and eglinazine.[21] It is used as an intermediate of the medicine such as thiamphenicol.[citation needed]

Laboratory research
Glycine is a significant component of some solutions used in the SDS-PAGE method of protein analysis. It serves as a buffering agent, maintaining pH and preventing sample damage during electrophoresis. Glycine is also used to remove protein-labeling antibodies from Western blot membranes to enable the probing of numerous proteins of interest from SDS-PAGE gel. This allows more data to be drawn from the same specimen, increasing the reliability of the data, reducing the amount of sample processing, and number of samples required. This process is known as stripping.

Presence in space
The presence of glycine outside the earth was confirmed in 2009, based on the analysis of samples that had been taken in 2004 by the NASA spacecraft Stardust from comet Wild 2 and subsequently returned to earth. Glycine had previously been identified in the Murchison meteorite in 1970.[35] The discovery of cometary glycine bolstered the theory of panspermia, which claims that the "building blocks" of life are widespread throughout the Universe.[36] In 2016, detection of glycine within Comet 67P/Churyumov-Gerasimenko by the Rosetta spacecraft was announced.[37]

The detection of glycine outside the solar system in the interstellar medium has been debated.[38] In 2008, the Max Planck Institute for Radio Astronomy discovered the spectral lines of a glycine-like molecule aminoacetonitrile in the Large Molecule Heimat, a giant gas cloud near the galactic center in the constellation Sagittarius.[39]

Presence in foods
Food sources of glycine[40]
Food g/100g
Snacks, pork skins 11.04
Sesame seeds flour (low fat) 3.43
Beverages, protein powder (soy-based) 2.37
Seeds, safflower seed meal, partially defatted 2.22
Meat, bison, beef and others (various parts) 1.5-2.0
Gelatin desserts1.96
Seeds, pumpkin and squash seed kernels 1.82
Turkey, all classes, back, meat and skin 1.79
Chicken, broilers or fryers, meat and skin 1.74
Pork, ground, 96% lean / 4% fat, cooked, crumbles 1.71
Bacon and beef sticks 1.64
Peanuts 1.63
Crustaceans, spiny lobster 1.59
Spices, mustard seed, ground 1.59
Salami 1.55
Nuts, butternuts, dried 1.51
Fish, salmon, pink, canned, drained solids 1.42
Almonds 1.42
Fish, mackerel 0.93
Cereals ready-to-eat, granola, homemade 0.81
Leeks, (bulb and lower-leaf portion), freeze-dried 0.7
Cheese, parmesan (and others), grated 0.56
Soybeans, green, cooked, boiled, drained, without salt 0.51
Bread, protein (includes gluten) 0.47
Egg, whole, cooked, fried 0.47
Beans, white, mature seeds, cooked, boiled, with salt 0.38
Lentils, mature seeds, cooked, boiled, with salt 0.37
See also
Amino acid neurotransmitter
Glycine is an amino acid, a building block for protein. It is not considered an "essential amino acid" because the body can make it from other chemicals. A typical diet contains about 2 grams of glycine daily. The primary sources are protein-rich foods including meat, fish, dairy, and legumes.

Glycine is used for treating schizophrenia, stroke, sleep problems, cystic fibrosis, benign prostatic hyperplasia (BPH), metabolic syndrome, and some rare inherited metabolic disorders. It is also used to protect kidneys from the harmful side effects of certain drugs used after organ transplantation as well as the liver from harmful effects of alcohol. Glycine may also be used to reduce the risk of psychosis. Other uses include cancer prevention and memory enhancement.

Some people apply glycine directly to the skin to treat leg ulcers and heal other wounds.

How does it work?
The body uses glycine to make proteins. Glycine is also involved in the transmission of chemical signals in the brain, so there is interest in trying it for schizophrenia and improving memory. Some researchers think glycine may have a role in cancer prevention because it seems to interfere with the blood supply needed by certain tumors.
Leg ulcers. Applying cream containing glycine and other amino acids seems to reduce pain and slightly improve the healing of leg ulcers.
Schizophrenia. Taking glycine by mouth along with conventional medicines seems to reduce certain symptoms of schizophrenia, called negative symptoms, in some people who don't respond to treatment with conventional medicines.
Stroke. Putting glycine under the tongue may help to limit brain damage caused by an ischemic stroke when started within 6 hours of having the stroke. An ischemic stroke is caused by the blockage of a blood vessel (usually by a clot) in the brain. Brain cells beyond the obstruction don't receive oxygen and begin to die, causing irreversible damage.
Taking glycine by mouth might reduce seizures in people with this condition.
Mental performance. Early research shows that taking glycine by mouth might improve memory and mental performance.
Cystic fibrosis. Early research shows that taking glycine by mouth might improve lung function and breathing by a small amount in patients with cystic fibrosis.
Taking glycine by mouth along with L-carnitine might help treat this condition.
Sleep quality. Taking glycine before bedtime for 2-4 days seems to improve sleep in people with poor sleep quality. Taking glycine before bedtime might also reduce feelings of tiredness the following day after a shortened night of sleep. But it doesn't seem to prevent tiredness after several shortened nights of sleep.
Glycine is an amino acid, one of 20 used to make proteins in the human body. The body produces it naturally.

Glycine is also found in high-protein foods such as:

Dairy products
It's estimated that we get about 2 grams of glycine a day from food sources. As a supplement, it's taken in much higher amounts.

Why do people take glycine?
Glycine has numerous proposed uses. Few of those suggested uses have enough evidence to fully back glycine's effectiveness.

Glycine has shown the most promise as a part of a treatment plan for schizophrenia. In several studies, glycine boosted the effectiveness of other schizophrenia drugs when taken at doses of .6 grams per kilogram of weight per day. However, glycine may have the opposite effect when paired with the antipsychotic drug clozapine (Clozaril, Versacloz).

A small study suggests that glycine may help people with type 2 diabetes control their blood sugar. But more research is needed to back up that result.

In a much larger study, small doses of glycine (1 to 2 grams dissolved under the tongue each day) showed some potential for limiting brain damage caused by ischemic stroke if treatment begins within several hours of a stroke. There is some concern, though, that high doses of glycine could make the damage caused by a stroke worse.

Studies done on animals hint at glycine's potential as an anticancer agent. But there's no evidence yet that it could help prevent or treat cancer in people. The same can be said for its ability to protect the liver and kidneys from damage caused by chemicals such as alcohol.

Leg ulcers, which can be caused by poor circulation, diabetes, kidney failure, and other health problems, have shown some improvement after treatment with a cream containing glycine and other amino acids.

One study showed some improvement in memory among young and middle-aged men. But the results need to be confirmed by more research.
Glycine is also marketed for a host of other uses, despite the lack of scientific evidence that it is effective or safe for any of them. For example, glycine is marketed as a way to:
Again, there is no reliable evidence that it works for such uses.

Optimal therapeutic doses for glycine have not been set for any condition. Also, as with supplements generally, the quality of the active ingredients in products that contain glycine varies from maker to maker.
What are the risks of taking glycine?
Glycine appears to be safe, even at doses of up to 9 grams for 3 days. But glycine's safety has not been fully tested or studied. Particular caution should be taken when considering glycine for young children, pregnant or breastfeeding women, and people with liver or kidney disease.
People being treated with clozapine should avoid taking glycine. Also people who have had a stroke should not take glycine without the supervision of a doctor.
A few people have reported nausea, vomiting, and upset stomach after taking glycine. Such reports have been rare, and the symptoms have gone away after glycine was discontinued.
Glycine is an excitatory amino acid that can modulate NMDA receptors and the glycine-binding site has been posited as a novel avenue for antidepressant treatment.42
Synthesis, Metabolism, and Anatomy
Glycine, a simple amino acid not essential to the human diet, acts not only as a powerful inhibitory neurotransmitter but also paradoxically as a co-agonist or modulator of the excitatory neurotransmitter glutamate at NMDA receptors. Hydroxymethyl transferase converts the amino acid serine to glycine.
Glycine's inhibitory activity acts on the motor neurons of the ventral horn of the spinal cord and the brainstem. Under normal circumstances, glycine provides inhibition of muscle tone that balances the excitation of muscle tone provided by other neurotransmitters. Several different metabolic pathways inactivate it.

Glycine oxidase (ThiO) catalyzes the oxidation of glycine (1) to the glycine imine 23. The ThiO structure, with N-acetylglycine bound at the active site, has been determined. This structure, as well as the efficient utilization of cyclopropyl glycine as a substrate, supports a hydride transfer mechanism (Figure 7).38
Glycine is a constituent of glutathione, an antioxidant tripeptide found in high concentrations in intestinal epithelial cells. The availability of glycine has potential to control the cellular levels of glutathione in enterocytes. There are two different transporters for glycine in mammalian cells, glycine transport 1 and 2 (GLYT1 and GLYT2).
Glycine is a constituent of glutathione, an antioxidant tripeptide found in high concentrations in intestinal epithelial cells. The availability of glycine controls the levels of glutathione in enterocytes. There are two different transporters for glycine in mammalian cells, namely
The main glycine receptor is a Cl-channel, so its activation will promote membrane hyperpolarization and reduce neuronal responsiveness. Glycine activity in the synapse is quenched by reuptake via specific transporters into presynaptic terminals and perisynaptic glial cells. The glia can release glycine, suggesting that glycine from this source may also serve as a neuromodulator. Some inhibitory synapses can simultaneously release GABA and glycine. During development, glycine may act transiently as an excitatory transmitter to help guide the maturation of CNS neurons.
Glycine has been used in whole-cell patch clamp recording to measure inward NMDA (N-methyl-D-aspartate) currents.[4] It has also been used as a model organic system in crystallography to demonstrate a novel acoustic nebulization platform.
Biochem/physiol Actions
Glycine is a non-essential amino acid.[1] Influx of calcium through the cell membrane is mediated by glycine-gated channel. Glycine participates in the synthesis of porphyrins, purine and serine. It also serves as a competitive agonist for glutamate in binding to the NMDA (N-methyl-D-aspartate) receptors.[2] Glycine synthesis might be increased in rapidly proliferating cancer cells, due to increased demand for the amino acid.[1]
Glycine, the simplest amino acid, obtainable by hydrolysis of proteins. Sweet-tasting, it was among the earliest amino acids to be isolated from gelatin (1820). Especially rich sources include gelatin and silk fibroin. Glycine is one of several so-called nonessential amino acids for mammals; i.e., they can synthesize it from the amino acids serine and threonine and from other sources and do not require dietary sources. The chemical structure of glycine is
You might not know it by name, but the tiny amino acid glycine is hard at work in your body right now, maintaining strength and support in your muscles and bones, helping keep your metabolism functioning right, supporting a healthy brain, and contributing to a good night's sleep.

For all its power to support the body's health and natural capacity for healing, glycine has gotten strangely little attention as a natural remedy. Let's take a look at some of what we know today about glycine-how it works in the body, and what additional glycine might do to affect your health and sleep.

What is glycine?

Glycine (also known as 2-Aminoacetic Acid) is an amino acid and a neurotransmitter. The body produces glycine on its own, synthesized from other natural biochemicals, most often serine, but also choline and threonine. We also consume glycine through food. This amino acid is found in high-protein foods including meat, fish, eggs, dairy and legumes. A daily diet typically includes about 2 grams of glycine.

Glycine is a neurotransmitter with the ability to be both excitatory and inhibitory, meaning it can function both to stimulate brain and nervous system activity, or to quiet it.

People use glycine as an oral supplement for a range of purposes, including improving sleep, enhancing memory, and increasing insulin sensitivity. Glycine is also available in topical form, and used to heal wounds and treat skin ulcers.

Glycine has a sweet taste, and is manufactured commercially as a sweetener and included in products such as cosmetics and antacids. Its name comes from the Greek word, glykys, which means "sweet."

Glycine is sometimes used in the treatment of schizophrenia, typically alongside conventional medication, to help reduce symptoms. Glycine is also given orally to patients who've suffered ischemic stroke (the most common type of stroke), as a treatment to help limit damage to the brain within the first six hours of the stroke.

How does Glycine work?

Glycine is considered among the most important amino acids for the body. It exerts widespread influence over our bodies' systems, structure, and general health, including cardiovascular, cognitive, and metabolic health. Here are some of the most important and well-understood roles that glycine plays in our health and functioning:

As an amino acid, glycine works as a protein builder in the body. In particular, glycine enables the production of collagen, a protein that is an essential component of muscles, tendon, skin, and bones. Collagen is the most commonly occurring protein in the body, comprising roughly a third of all body protein. It does no less than give the body its fundamental structure and strength. Collagen is the protein that helps skin maintain elasticity. Glycine also facilitates the production of creatine, a nutrient stored in and used by both the muscles and the brain for energy.
Glycine is involved in digestion, specifically in the breakdown of fatty acids in foods. It also helps maintain healthy levels of acidity in the digestive tract.

Glycine is also involved in the body's production of DNA and RNA, the genetic instructions that deliver our body's cells the information they need to function.

This amino acid helps to regulate blood sugar levels and move blood sugar to cells and tissues throughout the body, to be consumed as energy.

Glycine helps to regulate the body's immune response, to limit unhealthful inflammation and spur healing.

As a neurotransmitter, glycine both stimulates and inhibits cells in the brain and central nervous system, affecting cognition, mood, appetite and digestion, immune function, pain perception, and sleep. Glycine is also involved in the production of other biochemicals that influence these body functions. In particular, glycine helps the body make serotonin, a hormone and neurotransmitter that has significant effects on sleep and mood. It also influences key receptors in the brain that affect learning and memory.

Benefits of Glycine

For sleep: Glycine influences sleep in a number of ways. Studies show that higher levels of this amino acid may:

Help you fall asleep more quickly.
Increase your sleep efficiency.
Reduce symptoms of insomnia.
Improve sleep quality and promote deeper more restful sleep.
How does glycine accomplish all of this sleep-promoting work? It appears to affect sleep in at least a couple of important ways:

Glycine helps lower body temperature. Glycine works to increase blood flow to the body's extremities, which reduces core body temperature. I've written before about how the body's fluctuating temperature affects sleep-wake cycles, and your ability to initially fall asleep. A slight drop in body temp is a key part of the body's physical progression into sleep. A recent study of the effects of glycine as a supplement showed it triggered a drop in body temperature and at the same time helped people both fall asleep more quickly and spend more time in REM sleep. Other research has shown supplemental glycine may help you move more quickly into deep, slow wave sleep.
Glycine increases serotonin levels. Research shows oral glycine elevates serotonin, reduces symptoms of insomnia, and improves sleep quality.Glycine is active in the hippocampus, an area of the brain important for memory and learning. In supplement form, glycine appears to deliver benefits for daytime cognitive function. In the same study that showed supplemental glycine made it easier to fall asleep and get to slow-wave sleep, scientists also found people scored higher on daytime cognition tests. And supplemental glycine has been shown to improve both memory and attention in young adults. Scientists are actively investigating the use of glycine in the treatment of neurodegenerative disorders such as Alzheimer's disease.
Glycine works to support immune health and keep inflammation in check, offering protection to cardiovascular function. It also functions as an antioxidant, helping to trap and contain damaged cells that can cause disease. Higher levels of glycine have been associated with a lower risk of heart attack, and there's some evidence that glycine may help protect against high blood pressure. Still, the full relationship between glycine and cardiovascular health is something scientists are still working to better understand.
Glycine plays an important role in a healthy metabolism. Low levels of glycine are linked to greater risk for development of type 2 diabetes. On the other hand, higher glycine levels are associated with lower risk for this metabolic disorder. But it's not yet clear what the cause and effect are in this relationship: whether low glycine levels directly contribute to metabolic dysfunction that lead to diabetes, or whether they're a result of metabolic dysfunction already in progress. Studies show glycine can be effective in lowering blood sugar levels and increasing insulin production in healthy adults. In people with type 2 diabetes, studies have shown that glycine deficiencies can be improved by use of oral glycine. Other research suggests that in people with diabetes, oral glycine can lower blood sugar levels.
For sleep: A range of 3-5 grams of glycine taken orally before bed has been used effectively to help sleep in scientific studies.
For blood sugar: A range of 3-5 grams of glycine taken orally at meals has been used effectively to reduce blood sugar in scientific studies.
Glycine is generally well tolerated by healthy adults. Side effects are uncommon, but may include:
There are commonly used medications and supplements that have scientifically-identified interactions with glycine. People who take these or any other medications and supplements should consult with a physician before beginning to use glycine as a supplement.

Women who are pregnant or breastfeeding: It's recommended to avoid glycine use during pregnancy and breastfeeding,
Using glycine in combination with clozapine may reduce the effectiveness of clozapine. It's recommended people who are taking clozapine not use glycine.
When you talk to your physician about taking glycine, be sure to include information about the supplements you're already taking.

Glycine is a pretty fascinating natural biochemical, with benefits that stretch from physiological health, strength, and vitality, to more robust mental performance, to better sleep. Because of its wide-ranging impact, I expect we'll see increasing attention to how supplemental glycine can help us protect our health and our sleep.
Acide Aminoacétique, Acide Amino-Acétique, Aminoacetic Acid, Athenon, Free Base Glycine, G Salt, Glicina, Glycine de Base Libre, Glycocoll, Glycosthene, Iconyl, L-Glycine, Monazol.
Glycine is an amino acid, a building block for protein. It is not considered an "essential amino acid" because the body can make it from other chemicals. A typical diet contains about 2 grams of glycine daily. The primary sources are protein-rich foods including meat, fish, dairy, and legumes.
Glycine is used for treating schizophrenia, stroke, benign prostatic hyperplasia (BPH), and some rare inherited metabolic disorders. It is also used to protect kidneys from the harmful side effects of certain drugs used after organ transplantation as well as the liver from harmful effects of alcohol. Other uses include cancer prevention and memory enhancement.
Some people apply glycine directly to the skin to treat leg ulcers and heal other wounds.
Putting glycine under the tongue may help to limit brain damage caused by an ischemic stroke when started within 6 hours of having the stroke.
More evidence is needed to rate the effectiveness of glycine for these uses.
The body uses glycine to make proteins. Glycine is also involved in the transmission of chemical signals in the brain, so there is interest in trying it for schizophrenia and improving memory. Some researchers think glycine may have a role in cancer prevention because it seems to interfere with the blood supply needed by certain tumors.,
Glycine seems to be safe for most people when taken by mouth or applied to the skin. Most people do not experience side effects, although there have been a few reports of nausea, vomiting, stomach upset, and drowsiness.
aking glycine along with clozapine (Clozaril) might decrease the effectiveness of clozapine (Clozaril). It is not clear why this interaction occurs yet. Do not take glycine if you are taking clozapine (Clozaril).
Glycine is an amino acid and neurotransmitter. It can play both stimulatory and depressant roles in the brain. Supplementation can improve sleep quality.
There are improvements in cognition due to glycine being able to treat schizophrenia and due to glycine being able to improve sleep; two states of impaired cognition
The reduction in fatigue may solely be secondary to how Glycine supplementation can improve sleep quality
In persons undergoing mild sleep deprivation, 3g of glycine an hour prior to sleep is able to increase sleep quality and improve self-reports of fatigue and well being the next day due to better sleep.
Glycine is an amino acid that functions as a building block for certain proteins, most especially the collagen found in skin, ligaments, muscles, bones, and cartilage. It makes up around 35 percent of the collagen in the human body.

Glycine also helps regulate nerve impulses in the central nervous system, most specifically those of the spinal cord, retina, and the control center of the brain known as the brainstem. Glycine will also bind with toxic substances and aid in their excretion from the body.

Unlike other amino acids that are mainly derived from the foods we eat, glycine can be synthesized in the body and is therefore not considered an essential amino acid. We can obtain all the glycine we need from high-protein foods such as meat, poultry, fish, eggs, dairy, beans, cereals, and pasta.

With that being said, there is evidence that taking a glycine supplement can help treat certain medical conditions, both metabolic and neurological.
While some believe that glycine supplements act as "natural antidepressants," the effect on the brain is relatively short-lasting, causing a transient spike in serotonin levels that quickly dissipates within minutes.
The effect was dose-dependent, meaning that sleep patterns seemed to improve in tandem with increased glycine dosages, usually taken right before bedtime.While some proponents claim that glycine supplements can improve memory.
Although the presumption seems fair enough, there is little evidence that the strategy actually works. This is because the low glycine levels are no so much induced by the absence of glycine but rather by the rate at which glycine is metabolized in the liver as diabetes progresses.

As such, insulin resistance spurs the depletion of glycine, rather than the other way around. Increasing the intake of glycine will do little to alter this effect.
Glycine supplements are generally considered safe if taken as directed. With that said, there has been little research into the long-term safety of glycine supplements. Most people who take glycine will not experience any side effects. Those who do may have mild gastrointestinal symptoms such as an upset stomach, nausea, loose stools, or vomiting.

Glycine supplements are not recommended if you are taking the antipsychotic drug Clozaril (clozapine). Unlike other drugs used to treat schizophrenia, glycine appears to decrease the effectiveness of Clozaril in some people.
Role in structure: Glycine is a very unique amino acid in that in contains a hydrogen as its side chain (rather than a carbon as is the case in all other amino acids). This means that there is much more conformational flexibility in glycine. What this means is that glycine can reside in parts of protein structures that are forbidden to all other amino acids (e.g. tight turns in structures). Role in function: The uniqueness of Glycine also means that it can play a distinct functional role, such as using its sidechain-less backbone to bind to phosphates. This means that if one sees a conserved glycine changing to any other amino acid (i.e. even those listed above), the change could have an impact.
Glycine is a non-essential, neutral, genetically coded amino acid. It is the only protein-forming amino acid without a center of chirality.
Glycine is most important and simple, nonessential amino acid in humans, animals, and many mammals. Generally, glycine is synthesized from choline, serine, hydroxyproline, and threonine through interorgan metabolism in which kidneys and liver are the primarily involved. Generally in common feeding conditions, glycine is not sufficiently synthesized in humans, animals, and birds. Glycine acts as precursor for several key metabolites of low molecular weight such as creatine, glutathione, haem, purines, and porphyrins. Glycine is very effective in improving the health and supports the growth and well-being of humans and animals. There are overwhelming reports supporting the role of supplementary glycine in prevention of many diseases and disorders including cancer. Dietary supplementation of proper dose of glycine is effectual in treating metabolic disorders in patients with cardiovascular diseases, several inflammatory diseases, obesity, cancers, and diabetes. Glycine also has the property to enhance the quality of sleep and neurological functions. In this review we will focus on the metabolism of glycine in humans and animals and the recent findings and advances about the beneficial effects and protection of glycine in different disease states.
French chemist H. Braconnot was the first to isolate glycine from acid hydrolysates of protein in 1820 [1]. The taste of glycine is sweet like glucose, because of its sweet nature, and its name was derived from Greek word "glykys." Glycine is produced by alkaline hydrolysis of meat and gelatin with potassium hydroxide. A. Cahours chemically synthesized glycine from monochloroacetic acid and ammonia and established the structure of glycine [2]. Glycine is the simple amino acid with no L or D chemical configuration. The extracellular structural proteins such as elastin and collagen are made up of glycine. For mammals such as pigs, rodents, and human beings, glycine is treated as nutritionally nonessential amino acid. But some of the reports state that the quantity of glycine produced in vivo in pigs, rodents, and human beings is not adequate for the metabolic activity of them [3]. Shortage of glycine in small quantities is not harmful for health but severe shortage may lead to failure of immune response, low growth, abnormal nutrient metabolism, and undesirable effects on health [4]. Therefore, glycine is considered as a conditionally essential amino acid for humans and other mammals to enhance good growth. In case of birds, glycine is very essential requirement for neonatal and fetal growth, because neonates and fetuses cannot produce adequate glycine to meet required metabolic activities.
Glycine has very vital roles in metabolism and nutrition of many mammals and humans. Of the total amino acid content in human body, 11.5% is represented by glycine and 20% of the total amino acid nitrogen in body proteins is from glycine. Generally for growing human body or for other mammals, 80% of the whole body glycine is used for protein synthesis. In collagen, glycine is located at every third position; glycine residues bring together the triple helix of the collagen. The flexibility of active sites in enzymes is provided by glycine [5]. In central nervous system, glycine plays a crucial role as neurotransmitter, thereby controlling intake of food, behavior, and complete body homeostasis [6]. Glycine regulates the immune function, production of superoxide, and synthesis of cytokines by altering the intracellular Ca2+ levels [7]. The conjugation of bile acids in humans and pigs is facilitated by glycine; thereby glycine indirectly plays a crucial role in absorption and digestion of lipid soluble vitamins and lipids. RNA, DNA, creatine, serine, and haem are generated by several pathways which utilize glycine. Collectively, glycine has crucial function in cytoprotection, immune response, growth, development, metabolism, and survival of humans and many other mammals.
Some of the isotopic and nutritional investigations stated that glycine is synthesized in pigs, humans, and other mammals. The biochemical studies on rats proved that glycine is synthesized from threonine (through threonine dehydrogenase pathway), choline (via formation of sarcosine), and serine (through serine hydroxymethyltransferase [SHMT]). Later on, in other investigations it was proved that the glycine synthesis in pigs, humans, and other mammals is through the abovementioned three pathways [8]. From the recent studies it was stated that hydroxyproline and glyoxylate are substrates for glycine synthesis in humans and mammals [9, 10].
Methyl groups are generated in the mammalian tissues during degradation of choline to glycine. Generally in adult rats around 40-45% of the choline uptake is converted to glycine and this value can sometimes increases up to 70% when the choline uptake is very low. By conversion of choline to betaine by betaine aldehyde dehydrogenase and choline dehydrogenase [11], the three methyl groups of choline are readily available for three different conversions: (1) sarcosine into glycine by sarcosine dehydrogenase enzyme, (2) by using betaine from betaine-homocysteine methyltransferase as methyl donor and converting homocysteine into methionine, and (3) in conversion of dimethylglycine into sarcosine by dimethylglycine dehydrogenase enzyme. Sarcosine dehydrogenase and dimethylglycine dehydrogenase are the largely present in pancreas, lungs, liver, kidneys, oviduct, and thymus and these two enzymes are mitochondrial flavoenzymes [12]. Through transmethylation, glycine and sarcosine are interconvertible. Sarcosine dehydrogenase has very crucial role in glycine-sarcosine cycle, as it controls the ratio of S-adenosylhomocysteine to S-adenosylmethionine. The reactions involving the transfer of methyl group in cells are largely affected by S-adenosylhomocysteine to S-adenosylmethionine. If the content of choline in diet is very low, then glycine synthesis is quantitatively very low in mammals.
In young pigs, nearly 30% of the glycine supplied through diet is catabolized in the small intestine. Various types of bacterial strains present in the lumen of intestine are responsible for the degradation [24-26]. Degradation of glycine in humans and mammals is done via three pathways: (1) D-amino acid oxidase converting glycine into glyoxylate, (2) SHMT converting glycine into serine, and (3) deamination and decarboxylation by glycine cleavage enzyme system [27]. One carbon unit denoted by N5-N10-methylene tetrahydrofolate and the reversible action of serine formation from glycine is catalyzed by SHMT. Around 50% of the N5-N10-methylene tetrahydrofolate formed from the glycine cleavage enzyme system is used for serine synthesis from glycine. In primary cultures of mid gestation fetal hepatocytes and ovine fetal hepatocytes, nearly 30-50% of the extracellular glycine is used for serine biosynthesis [28, 29]. Different factors such as enzyme kinetics and intracellular concentration of products and substrates initiate the glycine cleavage enzyme system for oxidation of glycine than synthesis of glycine from CO2 and NH3. Mitochondrial glycine cleavage system [GCS] is vastly present in many mammals and humans; it is the main enzyme for degradation of glycine in their bodies [30]. But this enzyme is not present in the neurons. GCS catalyzes the interconversion of glycine into serine and it requires N5-N10-methylene tetrahydrofolate or tetrahydrofolate [31, 32]. The physiological importance of the GCS in degradation of glycine is characterized by its defect in humans which results in glycine encephalopathy and very high levels of plasma glycine. After phenylketonuria, glycine encephalopathy is the most frequently occurred inborn error of amino acid metabolism [33]. Metabolic acidosis, high protein diets, and glucagon increase glycine degradation and hepatic glycine cleavage activity in different mammals. But in the case of humans, high level of fatty acids in plasma suppresses the amount of glycine appearance and does not appear to influence glycine oxidation [34]. A sequential reaction of enzymes in the GCS in animal cells is explained in Figure 2.
It was reported that glycine is very effective to optimize the activities of g-glutamyltranspeptidase, alkaline phosphatases, asparatate transaminases, tissue fatty acid composition, and alanine transaminase, so oral supplementation of glycine can be very effective in protecting the alcohol-induced hepatotoxicity. Moreover glycine can optimize or change the lipid levels on chronic alcohol feeding by maintaining the integrity of membranes [35]. It was demonstrated that the rats supplemented with glycine showed very low blood alcohol levels. Iimuro et al. (2000) stated glycine as excellent preventive to reduce the alcohol levels in blood. Glycine has multiple effects such as reduction of accumulation of free fatty acids and regulates the individual free fatty acid composition in brain and liver of rats on chronic alcohol feeding. From the above evidences and reports it was proved that glycine is very effective and successful as a significant protective agent to fight against ethanol induced toxicity [36-38]. Glycine is known to reduce the rate of gastric emptying of ethanol; by this means it lowers the damage. In an animal model, the glycine supplementation reduced the lipids levels in alcohol-induced hyperlipidemia. From the scientific literature, it was proved that oral administration of glycine reduces the metabolic products of alcohol such as acetaldehyde from inducing the alteration in the carbohydrate moieties of glycoproteins. Glycine can also fight against free radical-mediated oxidative stress in hepatocytes, plasma, and erythrocyte membrane of humans and animals suffering from alcohol-induced liver injury [39]. From an in vivo study, it was demonstrated that certain melanomas like B16 and hepatic cancer can be prevented by glycine as it suppresses the endothelial cell proliferation and angiogenesis. Some of the other benefits of glycine are that it has cryoprotective effect in lethal cell injuries such as anoxia as it inhibits Ca2+-dependent degradation by nonlysosomal proteases including calpains [40]. Benign prostatic hyperplasia, schizophrenia, stroke, and some of the rare inherited metabolic disorders can be cured by glycine supplementation. The harmful effects of certain drugs on kidneys after organ transplantation can be protected by glycine diet. The dreadful effects of alcohol can be reduced by glycine. Glycine can be applied to skin to cure some wounds and ulcers in legs and it is most commonly used in treating ischemic stroke. Glycine exhibits prophylactic effect against hepatotoxicity. 2 g of glycine per day is required by the human body and it is to be supplied by diet. Legumes, fish, dairy products, and meat are some of the good sources of food. It has been reported that if glycine is injected intravenously before resuscitation, it lowers the mortality rate by reducing the organ injury in rats suffering from hemorrhagic shock [41]. Glycine supplemented orally reduces the endotoxic shock injuries caused by cyclosporine A and D-galactosamine [42].

Tumor necrosis factor, inflammation, and activation of macrophages are inhibited by glycine. Glycine also reduces alcohol-induced liver damage and removes lipid peroxidation reperfusion injury and glutathione deficiency caused by several types of hepatotoxins [43-45]. Some of the other functions of glycine are bile acid conjugation and chlorophyll production and it has vital role in many reactions such as haem, purine, and gluconeogenesis. Glycine along with alanine show special character to improve the alcohol metabolism. Glycine lowers the level of superoxide ions from neutrophils through glycine gated chloride channels. The chloride channels in Kupffer cells are activated by glycine and the activated Kupffer cells hyperpolarize the cell membrane and blunt intracellular Ca2+ concentrations; the similar functions are also carried out by glycine in neurons. If glycine is supplemented in large amounts it is toxic to human body. The major drawback of glycine oral supplementation is that it is quickly metabolized in the digestive system. Glycine enhances the first-pass removal of alcohol from the stomach thus preventing the alcohol from reaching the liver.
Jacob et al. (2003) reported that glycine protects the stomach from damage during the mesenteric ischemia by suppressing the apoptosis [46]. Lee et al. (2002) demonstrated that glycine gives protection against intestinal IR injury by a method consistent with uptake of glycine [47]. Intestine has several types of membrane transport systems which use glycine as the substrate to increase the cellular uptake. GLYT1 receptor is present in the basolateral membrane of enterocytes and its main function is to import glycine into the cells. The role of glycine in the cells is to look after the primary requirements of the enterocyte [48]. Howard et al. (2010) utilized human intestinal epithelial cell lines to study the function of GLYT1 in the cytoprotective effect of glycine to fight oxidative stress [49]. If glycine is given before the oxidative challenge, it protects the intracellular glutathione levels without disturbing the rate of glycine uptake. Protection of intracellular glutathione levels depends on the unique activity of GLYT1 receptor. GLYT1 receptor provides the necessary requirements for intracellular glycine accumulation.
Tsune et al. (2003) have reported that glycine has protected the intestinal injury caused by trinitrobenzene sulfonic acid or dextran sulfate sodium in chemical models of colitis.
The epithelial irritation and damage caused by the trinitrobenzene sulfonic acid or dextran sulfate sodium were cured by glycine [50]. Howard et al. (2010) reported that the direct effects of glycine on intestinal epithelial cells could show a particular influence on the complete inflammatory status of the intestine by significant change of redox status which is completely different from anti-inflammatory effects of glycine on several molecular targets of other mucosal cell populations. It was identified that 2 days of oral glycine supplementation after 2,4,6-trinitrobenzene sulfonic acid [TNBS] administration is very effective in lowering inflammation, which shows therapeutic and prophylactic benefits of glycine. The ability of glycine to change the multiple cell types further highlights the difficulty in dissecting the several modes of glycine function in reducing injury and inflammation. Glycine supplementation has very good efficacy in protecting against several intestinal disorders and further studies to investigate the specific roles of glycine receptors on epithelial cell and immune cells would help to understand the cytoprotective and anti-inflammatory effects of glycine.
his organ transplantation failure can be prevented by glycine therapy. Cold and hypoxic ischemic injuries of rabbit and dogs kidneys were cured by glycine and glycine treatment improved the graft function transplantation [51]. Moreover, kidneys rinsed in glycine containing Carolina solution can be protected against reperfusion injury or storage injury and enhance renal graft function and long survival after kidney transplantation [52]. The usage of glycine in organ transplantation is most widely investigated in liver transplantation. Addition of glycine to Carolina rinse solution and cold storage solution not only cures the storage injury/reperfusion injury but also enhances the graft function and health by decreasing the nonparenchymal cell injury in rat liver transplantation [53, 54]. Intravenous injection of glycine to donor rats will effectively increase the survival rate of graft.
Glycine improves the survival and reduces the organ injury after resuscitation or hemorrhage shock in a dose-dependent manner. In another investigation it was proved that glycine effectively reduces transaminase release, mortality, and hepatic necrosis after hemorrhage shock [62]. The endotoxin treatment triggers hepatic necrosis, lung injury, increased serum transaminase levels, and mortality which can be cured by short term glycine treatment. Constant treatment with glycine for four weeks decreases inflammation and enhances survival after endotoxin but does not improve liver pathology [63]. The specific effect after constant glycine treatment is due to downregulation of glycine gated chloride channels on Kupffer cells but not on neutrophils and alveolar macrophages. Glycine has the property to improve the survival rate by decreasing lung inflammation. Glycine improves function of liver, cures liver injury, and prevents mortality in experimental sepsis caused by cecal puncture and ligation. From the scientific literature it is clear that glycine is very potent in protecting septic, endotoxin, and hemorrhagic shock [64].
Acid secretions caused by pylorus ligation are decreased by glycine. Glycine also protects against experimental gastric lesions in rats caused by indomethacin, hypothermic-restraint stress, and necrotizing agents such as 0.6 M hydrochloric acid, 0.2 M sodium hydroxide, and 80% ethanol [65]. Glycine possesses effective cytoprotective and antiulcer activity. Moreover, further studies are very essential to explain the mechanisms of glycine action on the stomach disorders and to find out its role in the treatment and prophylaxis of gastric ulcer disease.
Glycine has much important physiological function in humans and animals. Glycine is precursor for a variety of important metabolites such as glutathione, porphyrins, purines, haem, and creatine




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