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Glycine (symbol Gly or G[4]) (/ˈɡlʌɪsn/)[5] is the amino acid that has a single hydrogen atom as its side chain. It is the simplest possible amino acid. The chemical formula of glycine is NH2CH2COOH. Glycine is one of the proteinogenic amino acids. In the genetic code, all codons starting with GG, namely GGU, GGC, GGA, GGG, code for glycine.

Glycin - Glycine.svg
Canonical amino acid form
Zwitterion of glycine
Zwitterionic form at physiological pH
Preferred IUPAC name
Systematic IUPAC name
Aminoethanoic acid
Other names
Aminoacetic acid
3D model (JSmol)
Abbreviations Gly, G
ECHA InfoCard 100.000.248
EC Number 200-272-2
Molar mass 75.07 g·mol−1
Appearance White solid
Density 1.607 g/cm3
Melting point 233 °C (451 °F; 506 K) (decomposition)
24.99 g/100 mL (25 °C)[2]
Solubility soluble in pyridine
sparingly soluble in ethanol
insoluble in ether
Acidity (pKa) 2.34 (carboxyl), 9.6 (amino)[3]
-40.3·10−6 cm3/mol
B05CX03 (WHO)
Safety data sheet See: data page
Lethal dose or concentration (LD, LC):
2600 mg/kg (mouse, oral)
Supplementary data page
Refractive index (n),
Dielectric constantr), etc.
Phase behaviour
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
YesY verify (what is YesYN ?)
Infobox references

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.

Glycine is a white crystalline solid


History and etymologyEdit

Glycine was discovered in 1820 by Henri Braconnot when he hydrolyzed gelatin by boiling it with sulfuric acid.[6] He originally called it "sugar of gelatin",[7] but a student of Liebig showed that it contained Nitrogen, and Berzelius renamed it "glycine".[8] The name comes from the Greek word γλυκύς "sweet tasting"[9] (which is also related to the prefixes glyco- and gluco-, as in glycoprotein and glucose). Another early name for glycine was "glycocoll".[10]


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.[11] The two main processes are amination of chloroacetic acid with ammonia, giving glycine and ammonium chloride,[12] and the Strecker amino acid synthesis,[13] which is the main synthetic method in the United States and Japan.[14] About 15 thousand tonnes are produced annually in this way.[15]

Glycine is also cogenerated as an impurity in the synthesis of EDTA, arising from reactions of the ammonia coproduct.[16]

Acid-base propertiesEdit


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 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.[17] In most organisms, the enzyme serine hydroxymethyltransferase catalyses this transformation via the cofactor pyridoxal phosphate:[18]

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:[18]

CO2 + NH+
+ 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:[18]

Glycine + tetrahydrofolate + NAD+ ⇌ CO2 + NH+
+ 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.[18]

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.[18]

The half-life of glycine and its elimination from the body varies significantly based on dose.[19] In one study, the half-life varied between 0.5 and 4.0 hours.[19]

Physiological functionEdit

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.[18][20] In the genetic code, glycine is coded by all codons starting with GG, namely GGU, GGC, GGA and GGG.

As a biosynthetic intermediateEdit

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.[18]

As a neurotransmitterEdit

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.[21] The LD50 of glycine is 7930 mg/kg in rats (oral),[22] 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. Where the customer’s purity requirements exceed the minimum required under the USP standard, for example for some pharmaceutical applications such as intravenous injections, pharmaceutical grade glycine, often produced to proprietary specifications and typically sold at a premium over USP grade glycine, may 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.[23]

Animal and human foodsEdit

USP glycine has a wide variety of uses, including as an additive in pet food and animal feed, in foods and pharmaceuticals as a sweetener/taste enhancer, or as a component of food supplements and protein drinks.

Two glycine molecules in a dipeptide form (Diglycinate) are sometimes used as a way to enhance the absorption of mineral supplementation since, only when bound to a dipeptide, can be absorbed through a different set of transporters.[24]

Cosmetics and miscellaneous applicationsEdit

Glycine serves as a buffering agent in antacids, analgesics, antiperspirants, cosmetics, and toiletries.

A variety of industrial and chemical processes use glycine or its derivatives, such as the production of fertilizers and metal complexing agents.[25]

Chemical feedstockEdit

Glycine is an intermediate in the synthesis of a variety of chemical products. It is used in the manufacture of the herbicide glyphosate.[26]

Laboratory researchEdit

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 spaceEdit

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.[27] The discovery of cometary glycine bolstered the theory of panspermia, which claims that the "building blocks" of life are widespread throughout the Universe.[28] In 2016, detection of glycine within Comet 67P/Churyumov-Gerasimenko by the Rosetta spacecraft was announced.[29]

The detection of glycine outside the solar system in the interstellar medium has been debated.[30] In 2008, the Max Planck Institute for Radio Astronomy discovered the glycine-like molecule aminoacetonitrile in the Large Molecule Heimat, a giant gas cloud near the galactic center in the constellation Sagittarius.[31]

See alsoEdit


  1. ^ The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals (11th ed.), Merck, 1989, ISBN 091191028X , 4386.
  2. ^ "Solubilities and densities". Retrieved 2013-11-13. 
  3. ^ Dawson, R.M.C., et al., Data for Biochemical Research, Oxford, Clarendon Press, 1959.
  4. ^ "Nomenclature and Symbolism for Amino Acids and Peptides". IUPAC-IUB Joint Commission on Biochemical Nomenclature. 1983. Archived from the original on 9 October 2008. Retrieved 5 March 2018. 
  5. ^
  6. ^ R.H.A. Plimmer (1912) [1908]. R.H.A. Plimmer; F.G. Hopkins, eds. The chemical composition of the proteins. Monographs on biochemistry. Part I. Analysis (2nd ed.). London: Longmans, Green and Co. p. 82. Retrieved January 18, 2010. 
  7. ^ MacKenzie, Colin (1822). One Thousand Experiments in Chemistry: With Illustrations of Natural Phenomena; and Practical Observations on the Manufacturing and Chemical Processes at Present Pursued in the Successful Cultivation of the Useful Arts ... Sir R. Phillips and Company. 
  8. ^ Nye, Mary Jo (1999). Before Big Science: The Pursuit of Modern Chemistry and Physics, 1800-1940. Harvard University Press. ISBN 9780674063822. 
  9. ^ "glycine". Oxford Dictionaries. Retrieved 2015-12-06. 
  10. ^ Ihde, Aaron J. (1970). The Development of Modern Chemistry. Courier Corporation. ISBN 9780486642352. 
  11. ^ Okafor, Nduka (2016-03-09). Modern Industrial Microbiology and Biotechnology. CRC Press. ISBN 9781439843239. 
  12. ^ Ingersoll, A. W.; Babcock, S. H. (1932). "Hippuric acid". Organic Syntheses. 12: 40. ; Collective Volume, 2, p. 328 
  13. ^ Wiley (2007-12-14). Kirk-Othmer Food and Feed Technology, 2 Volume Set. John Wiley & Sons. ISBN 9780470174487. 
  14. ^ "Glycine Conference (prelim)". USITC. Archived from the original on 2012-02-22. Retrieved 2014-06-13. 
  15. ^ Drauz, Karlheinz; Grayson, Ian; Kleemann, Axel; Krimmer, Hans-Peter; Leuchtenberger, Wolfgang and Weckbecker, Christoph (2007) "Amino Acids" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. doi:10.1002/14356007.a02_057.pub2
  16. ^ Hart, J. Roger (2005) "Ethylenediaminetetraacetic Acid and Related Chelating Agents" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. doi:10.1002/14356007.a10_095
  17. ^ Meléndez-Hevia, E; De Paz-Lugo, P; Cornish-Bowden, A; Cárdenas, M. L. (December 2009). "A weak link in metabolism: the metabolic capacity for glycine biosynthesis does not satisfy the need for collagen synthesis". Journal of biosciences. 34 (6): 853–72. doi:10.1007/s12038-009-0100-9. PMID 20093739. 
  18. ^ a b c d e f g Nelson, David L.; Cox, Michael M. (2005), Principles of Biochemistry (4th ed.), New York: W. H. Freeman, pp. 127, 675–77, 844, 854, ISBN 0-7167-4339-6 
  19. ^ a b Hahn RG (1993). "Dose-dependent half-life of glycine". Urological Research. 21 (4): 289–291. doi:10.1007/BF00307714. PMID 8212419. 
  20. ^ Szpak, Paul (2011). "Fish bone chemistry and ultrastructure: implications for taphonomy and stable isotope analysis". Journal of Archaeological Science. 38 (12): 3358–3372. doi:10.1016/j.jas.2011.07.022. 
  21. ^ "Recent development in NMDA receptors". Chinese Medical Journal. 2000. 
  22. ^ "Safety (MSDS) data for glycine". The Physical and Theoretical Chemistry Laboratory Oxford University. 2005. Retrieved 2006-11-01. 
  23. ^ "Glycine From Japan and Korea" (PDF). U.S. International Trade Commission. January 2008. Retrieved 2014-06-13. 
  24. ^ Kurtis, Frank,; Kamal, Patel,; Gregory, Lopez,; Bill, Willis, (2017-08-01). "Glycine Research Analysis". 
  25. ^ "Notice of Preliminary Determination of Sales at Less Than Fair Value: Glycine From India" Federal Register 72 (7 November 2007): 62827.
  26. ^ Stahl, Shannon S.; Alsters, Paul L. (2016-07-13). Liquid Phase Aerobic Oxidation Catalysis: Industrial Applications and Academic Perspectives. John Wiley & Sons. ISBN 9783527690152. 
  27. ^ Kvenvolden, Keith A.; Lawless, James; Pering, Katherine; Peterson, Etta; Flores, Jose; Ponnamperuma, Cyril; Kaplan, Isaac R.; Moore, Carleton (1970). "Evidence for extraterrestrial amino-acids and hydrocarbons in the Murchison meteorite". Nature. 228 (5275): 923–926. Bibcode:1970Natur.228..923K. doi:10.1038/228923a0. PMID 5482102. 
  28. ^ Reuters (18 August 2009). "Building block of life found on comet - Thomson Reuters 2009". Retrieved 2009-08-18. 
  29. ^ European Space Agency (27 May 2016). "Rosetta's comet contains ingredients for life". Retrieved 2016-06-05. 
  30. ^ 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. 
  31. ^ Staff. "Organic Molecule, Amino Acid-Like, Found In Constellation Sagittarius 27 March 2008 - Science Daily". Retrieved 2008-09-16. 

Further readingEdit

External linksEdit