|Jmol 3D model||Interactive image|
|Molar mass||75.07 g/mol|
|Melting point||233 °C (451 °F; 506 K) (decomposition)|
|24.99 g/100 mL (25 °C)|
|Solubility||soluble in pyridine
sparingly soluble in ethanol
insoluble in ether
|Acidity (pKa)||2.34 (carboxyl), 9.6 (amino)|
|Safety data sheet||See: data page|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
|2600 mg/kg (mouse, oral)|
|Supplementary data page|
|Refractive index (n),
Dielectric constant (εr), etc.
|UV, IR, NMR, MS|
|what is ?)(|
Glycine (abbreviated as Gly or G) is the smallest of the 20 amino acids commonly found in proteins, and indeed is the smallest possible (having a hydrogen substituent as its side-chain). The formula is NH2CH2COOH. Its codons are GGU, GGC, GGA, GGG of the genetic code.
Glycine is a colorless, sweet-tasting crystalline solid. It is unique among the proteinogenic amino acids in that it is achiral. It can fit into hydrophilic or hydrophobic environments, due to its minimal side chain of only one hydrogen atom. The acyl radical is glycyl.
- 1 History and etymology
- 2 Production
- 3 Acid-base properties and structures
- 4 Metabolism
- 5 Physiological function
- 6 Uses
- 7 Presence in space
- 8 See also
- 9 References
- 10 Further reading
- 11 External links
History and etymology
Glycine was first isolated from gelatin in 1820. The name comes from the ancient Greek word γλυκύς "sweet tasting" (which is also related to the prefixes glyco- and gluco-, as in glycoprotein and glucose).
- ClCH2COOH + 2 NH3 → H2NCH2COOH + NH4Cl
About 15 million kg are produced annually in this way.
There are two producers of glycine in the United States: Chattem Chemicals, Inc., a subsidiary of Mumbai-based Sun Pharmaceutical, and GEO Specialty Chemicals, Inc., which purchased the glycine and naphthalene sulfonate production facilities of Hampshire Chemical Corp, a subsidiary of Dow Chemical.
Chattem's manufacturing process ("MCA" process) occurs in batches and results in a finished product with some residual chloride but no sulfate, while GEO’s manufacturing process is considered a semi-batch process and results in a finished product with some residual sulfate but no chloride.
Acid-base properties and structures
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). The nature of glycine in aqueous solution has been investigated by theoretical methods. In solution the ratio of concentrations of the two isomers is independent of both the analytical concentration and of pH. This ratio is simply the equilibrium constant for isomerization.
- K = [NH3+CH2CO2-]/[H2NCH2CO2H]
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. In most organisms, the enzyme serine hydroxymethyltransferase catalyses this transformation via the cofactor pyridoxal phosphate:
- serine + tetrahydrofolate → glycine + N5,N10-Methylene tetrahydrofolate + H2O
- CO2 + NH4+ + N5,N10-Methylene tetrahydrofolate + NADH + H+ → Glycine + tetrahydrofolate + NAD+
- Glycine + tetrahydrofolate + NAD+ → CO2 + NH4+ + 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.
In the third pathway of glycine 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.
The half-life of glycine and its elimination from the body varies significantly based on dose. In one study, the half-life was between 0.5 and 4.0 hours. 
The principal function of glycine is as a precursor to proteins, such as its periodically repeated role in the formation of the collagen helix in conjunction with hydroxyproline. It is also a building block for numerous natural products.
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.
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. The LD50 of glycine is 7930 mg/kg in rats (oral), and it usually causes death by hyperexcitability.
A 2014 review on sleep aids noted that glycine can improve sleep quality, citing a study in which 3 grams of glycine before bedtime improved sleep quality in humans. Glycine has also been positively tested as an add-on treatment for schizophrenia.
In the US, glycine is typically sold in two grades: United States Pharmacopeia (“USP”), and technical grade. Most glycine is manufactured as USP grade material for diverse uses. USP grade sales account for approximately 80 to 85 percent of the U.S. market for glycine.
- Pharmaceutical grade glycine is produced for some pharmaceutical applications, such as intravenous injections, where the customer’s purity requirements often exceed the minimum required under the USP grade designation. Pharmaceutical grade glycine is often produced to proprietary specifications and is typically sold at a premium over USP grade glycine.
- Technical grade glycine, which may or may not meet USP grade standards, is sold for use in industrial applications; e.g., as an agent in metal complexing and finishing. Technical grade glycine is typically sold at a discount to USP grade glycine.
Animal and human foods
Other markets for USP grade glycine include its use an additive in pet food and animal feed. For humans, glycine is sold as a sweetener/taste enhancer. Certain food supplements and protein drinks contain glycine. Certain drug formulations include glycine to improve gastric absorption of the drug.
Cosmetics and miscellaneous applications
Many miscellaneous products use glycine or its derivatives, such as the production of rubber sponge products, fertilizers, metal complexants.
Glycine is an intermediate in the synthesis of a variety of chemical products. It is used in the manufacture of the herbicide glyphosate.
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
In 2009, glycine sampled in 2004 from comet Wild 2 by the NASA spacecraft Stardust was confirmed – the first discovery of glycine outside the Earth, although glycine had been identified in the Murchison meteorite in 1970. The discovery of cometary glycine bolstered the theory of panspermia, which claims that the "building-blocks" of life are widespread throughout the Universe. In 2016, detection of glycine within Comet 67P/Churyumov-Gerasimenko by the Rosetta spacecraft was announced.
The detection of glycine outside the solar system in the interstellar medium has been debated. In 2008, the glycine-like molecule aminoacetonitrile was discovered in the Large Molecule Heimat, a giant gas cloud near the galactic center in the constellation Sagittarius by the Max Planck Institute for Radio Astronomy.
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Glycine (a non-essential amino acid) functions as an inhibitory neurotransmitter in the central nervous system and also acts as a co-agonist of glutamate receptors. In a Japanese study , glycine has been shown to improve subjective sleep. Yamadera et al.  also reported shorter sleep-onset latencies measured by polysomnography. The authors suggested that potential mechanisms involve increased vasodilation and thus lowering of core temperature and increased extracellular 5-HT release in the prefrontal cortex of rats 
- Yamadera W, Inagawa K, Chiba S, Bannai M, Takahashi M, Nakayama K (2007). "Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes". Sleep and Biological rhythms 5 (2): 126–131. doi:10.1111/j.1479-8425.2007.00262.x.
- Coyle JT; G Tsai (2004). "The NMDA receptor glycine modulatory site: a therapeutic target for improving cognition and reducing negative symptoms in schizophrenia". Psychopharmacology 174: 32–28. doi:10.1007/s00213-003-1709-2.
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- Reuters (18 August 2009). "Building block of life found on comet - Thomson Reuters 2009". Retrieved 2009-08-18.
- European Space Agency (27 May 2016). "Rosetta’s comet contains ingredients for life". Retrieved 2016-06-05.
- Snyder LE, Lovas FJ, Hollis JM, et al. (2005). "A rigorous attempt to verify interstellar glycine". Astrophys J 619 (2): 914–930. arXiv:astro-ph/0410335. Bibcode:2005ApJ...619..914S. doi:10.1086/426677.
- Staff. "Organic Molecule, Amino Acid-Like, Found In Constellation Sagittarius 27 March 2008 - Science Daily". Retrieved 2008-09-16.
On attempts to detect glycine in interstellar medium
- Kuan YJ, Charnley SB, Huang HC, et al. (2003). "Interstellar glycine". Astrophys J 593 (2): 848–867. Bibcode:2003ApJ...593..848K. doi:10.1086/375637.
- Rachel Nowak. "Amino acid found in deep space - 18 July 2002 - New Scientist". Retrieved 2007-07-01.
|Wikimedia Commons has media related to Glycine.|
- Glycine MS Spectrum
- Glycine at PDRHealth.com
- Glycine cleavage system
- Glycine Therapy - A New Direction for Schizophrenia Treatment?
- "Organic Molecule, Amino Acid-Like, Found In Constellation Sagittarius". ScienceDaily. 27 March 2008.
- Guochuan E. Tsai (1 December 2008). "A New Class of Antipsychotic Drugs: Enhancing Neurotransmission Mediated by NMDA Receptors". Psychiatric Times 25 (14).
- ChemSub Online (Glycine).
- NASA scientists have discovered glycine, a fundamental building block of life, in samples of comet Wild 2 returned by NASA's Stardust spacecraft.