Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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 formulaNH2‐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 achiralproteinogenic 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.
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:
H 3N+ CH 2COO− + 3 CH3I → (CH 3) 3N+ CH 2COO− + 3 HI
Glycine condenses with itself to give peptides, beginning with the formation of glycylglycine:
2 H 3N+ CH 2COO− → H 3N+ CH 2CONHCH 2COO− + H2O
Pyrolysis of glycine or glycylglycine gives 2,5-diketopiperazine, the cyclic diamide.
In addition to being synthesized from serine, glycine can also be derived from threonine, choline or hydroxyproline via inter-organ metabolism of the liver and kidneys.[27]
Degradation
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]
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]
The half-life of glycine and its elimination from the body varies significantly based on dose.[28] In one study, the half-life varied between 0.5 and 4.0 hours.[28]
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.[29]
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][30] In the genetic code, glycine is coded by all codons starting with GG, namely GGU, GGC, GGA and GGG.
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.[33]
Glycine is not widely used in foods for its nutritional 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 herbicidesglyphosate,[35]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.[36] The discovery of cometary glycine bolstered the theory of panspermia, which claims that the "building blocks" of life are widespread throughout the Universe.[37] In 2016, detection of glycine within Comet 67P/Churyumov-Gerasimenko by the Rosetta spacecraft was announced.[38]
Several independent evolutionary studies using different types of data have suggested that glycine belongs to a group of amino acids that constituted the early genetic code.[41][42][43][44] For example, low complexity regions (in proteins), that may resemble the proto-peptides of the early genetic code are highly enriched in glycine.[44]
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^Braconnot, Henri (1820). "Sur la conversion des matières animales en nouvelles substances par le moyen de l'acide sulfurique" [On the conversion of animal materials into new substances by means of sulfuric acid]. Annales de Chimie et de Physique. 2nd series (in French). 13: 113–125. ; see p. 114.
^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. p. 557.
^Boussingault (1838). "Sur la composition du sucre de gélatine et de l'acide nitro-saccharique de Braconnot" [On the composition of sugar of gelatine and of nitro-glucaric acid of Braconnot]. Comptes Rendus (in French). 7: 493–495.
^Horsford, E.N. (1847). "Glycocoll (gelatine sugar) and some of its products of decomposition". The American Journal of Science and Arts. 2nd series. 3: 369–381.
^Ihde, Aaron J. (1970). The Development of Modern Chemistry. Courier Corporation. ISBN 9780486642352.
^Berzelius, Jacob (1848). Jahres-Bericht über die Fortschritte der Chemie und Mineralogie (Annual Report on the Progress of Chemistry and Mineralogy). vol. 47. Tübigen, (Germany): Laupp. p. 654. From p. 654: "Er hat dem Leimzucker als Basis den Namen Glycocoll gegeben. … Glycin genannt werden, und diesen Namen werde ich anwenden." (He [i.e., the American scientist Eben Norton Horsford, then a student of the German chemist Justus von Liebig] gave the name "glycocoll" to Leimzucker [sugar of gelatine], a base. This name is not euphonious and has besides the flaw that it clashes with the names of the rest of the bases. It is compounded from γλυχυς (sweet) and χολλα (animal glue). Since this organic base is the only [one] which tastes sweet, then it can much more briefly be named "glycine", and I will use this name.)
^Nye, Mary Jo (1999). Before Big Science: The Pursuit of Modern Chemistry and Physics, 1800-1940. Harvard University Press. ISBN 9780674063822.
^Cahours, A. (1858). "Recherches sur les acides amidés" [Investigations into aminated acids]. Comptes Rendus (in French). 46: 1044–1047.
^Okafor, Nduka (2016-03-09). Modern Industrial Microbiology and Biotechnology. CRC Press. ISBN 9781439843239.
^Ingersoll, A. W.; Babcock, S. H. (1932). "Hippuric acid". Organic Syntheses. 12: 40.; Collective Volume, 2, p. 328
^Wiley (2007-12-14). Kirk-Othmer Food and Feed Technology, 2 Volume Set. John Wiley & Sons. ISBN 9780470174487.
^"Glycine Conference (prelim)". USITC. Archived from the original on 2012-02-22. Retrieved 2014-06-13.CS1 maint: bot: original URL status unknown (link)
^ abcDrauz, Karlheinz; Grayson, Ian; Kleemann, Axel; Krimmer, Hans-Peter; Leuchtenberger, Wolfgang & Weckbecker, Christoph (2007). "Amino Acids". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH.
^Ingersoll, A. W.; Babcock, S. H. (1932). "Hippuric Acid". Org. Synth. 12: 40. doi:10.15227/orgsyn.012.0040.
^Herbst, R. M.; Shemin, D. (1939). "Acetylglycine". Org. Synth. 19: 4. doi:10.15227/orgsyn.019.0004.
^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. PMID20093739. S2CID 2786988.
^ abcdefgNelson, 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.
^ACS Chem Biol. 2010 Aug 20; 5(8): 787–795.
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^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.
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^Casari, B. M.; Mahmoudkhani, A. H.; Langer, V. (2004). "A Redetermination of cis-Aquabis(glycinato-κ2N,O)copper(II)". Acta Crystallogr. E. 60 (12): m1949–m1951. doi:10.1107/S1600536804030041.
^Stahl, Shannon S.; Alsters, Paul L. (2016-07-13). Liquid Phase Aerobic Oxidation Catalysis: Industrial Applications and Academic Perspectives. John Wiley & Sons. ISBN 9783527690152.
^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. PMID5482102. S2CID 4147981.
^"Building block of life found on comet - Thomson Reuters 2009". Reuters. 18 August 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. S2CID 16286204.
^Staff. "Organic Molecule, Amino Acid-Like, Found In Constellation Sagittarius 27 March 2008 - Science Daily". Retrieved 2008-09-16.
^Trifonov, E.N (December 2000). "Consensus temporal order of amino acids and evolution of the triplet code". Gene. 261 (1): 139–151. doi:10.1016/S0378-1119(00)00476-5. PMID11164045.
^Higgs, Paul G.; Pudritz, Ralph E. (June 2009). "A Thermodynamic Basis for Prebiotic Amino Acid Synthesis and the Nature of the First Genetic Code". Astrobiology. 9 (5): 483–490. arXiv:0904.0402. Bibcode:2009AsBio...9..483H. doi:10.1089/ast.2008.0280. ISSN 1531-1074. PMID19566427. S2CID 9039622.
^Chaliotis, Anargyros; Vlastaridis, Panayotis; Mossialos, Dimitris; Ibba, Michael; Becker, Hubert D.; Stathopoulos, Constantinos; Amoutzias, Grigorios D. (2017-02-17). "The complex evolutionary history of aminoacyl-tRNA synthetases". Nucleic Acids Research. 45 (3): 1059–1068. doi:10.1093/nar/gkw1182. ISSN 0305-1048. PMC5388404. PMID28180287.
^ abNtountoumi, Chrysa; Vlastaridis, Panayotis; Mossialos, Dimitris; Stathopoulos, Constantinos; Iliopoulos, Ioannis; Promponas, Vasilios; Oliver, Stephen G; Amoutzias, Grigoris D (2019-11-04). "Low complexity regions in the proteins of prokaryotes perform important functional roles and are highly conserved". Nucleic Acids Research. 47 (19): 9998–10009. doi:10.1093/nar/gkz730. ISSN 0305-1048. PMC6821194. PMID31504783.
^"National Nutrient Database for Standard Reference". U.S. Department of Agriculture. Archived from the original on 2015-03-03. Retrieved 2009-09-07. Cite journal requires |journal= (help)
Further reading
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.
Nowak, Rachel. "Amino acid found in deep space - 18 July 2002 - New Scientist". Retrieved 2007-07-01.
External links
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.
Tsai, Guochuan E. (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.