View source for Glycine

{{short description|Amino acid}}
{{cs1 config|name-list-style=vanc|display-authors=6}}
{{Other uses}}
{{Distinguish|Glycerin}}
{{Use mdy dates|date=August 2022}}
{{chembox
| Watchedfields  = changed
| verifiedrevid  = 464190930
| Reference      = <ref>{{Merck11th|4386}}</ref>
| ImageFileL1    = Glycine-2D-skeletal.svg
| ImageSizeL1    = 120px
| ImageCaptionL1 = [[Skeletal formula]] of neutral glycine
| ImageFileR1    = Glycine-zwitterion-2D-skeletal.svg
| ImageSizeR1    = 120px
| ImageCaptionR1 = Skeletal formula of [[zwitterion]]ic glycine
| ImageFileL2    = Glycine-neutral-Ipttt-conformer-3D-bs-17.png
| ImageSizeL2    = 120px
| ImageCaptionL2 = [[Ball-and-stick model]] of the gas-phase structure
| ImageFileR2    = Glycine-zwitterion-from-xtal-3D-bs-17.png
| ImageSizeR2    = 120px
| ImageCaptionR2 = Ball-and-stick model of the zwitterionic solid-state structure
| ImageFileL3    = Glycine-neutral-Ipttt-conformer-3D-sf.png
| ImageSizeL3    = 120px
| ImageCaptionL3 = [[Space-filling model]] of the gas-phase structure
| ImageFileR3    = Glycine-zwitterion-from-xtal-3D-sf.png
| ImageSizeR3    = 120px
| ImageCaptionR3 = Space-filling model of the zwitterionic solid-state structure
<!-- | ImageCaptionL2 = Canonical amino acid form
     | ImageCaptionR2 = [[Zwitterion]]ic form at physiological pH 
 -->
| IUPACName      = Glycine
| SystematicName = Aminoacetic acid<ref>pubchem.ncbi.nlm.nih.gov/compound/750#section=IUPAC-Name&fullscreen=true</ref>
| OtherNames     = {{Unbulleted list
  | 2-Aminoethanoic acid
  | Glycocol
  | Glycic acid
  | Dicarbamic acid
  }}
| Section1       = {{Chembox Identifiers
| Abbreviations = '''Gly''', '''G'''
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = TE7660XO1C
| UNII2_Ref     = {{fdacite|correct|FDA}}
| UNII2         = 225ZLC74HX
| ChEMBL_Ref = {{ebicite|correct|EBI}}
| ChEMBL = 773
| KEGG_Ref = {{keggcite|correct|kegg}}
| KEGG = D00011
| InChI = 1S/C2H5NO2/c3-1-2(4)5/h1,3H2,(H,4,5)
| InChIKey = DHMQDGOQFOQNFH-UHFFFAOYAW
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/C2H5NH2/c3-1-2(4)5/h1,3H2,(H,4,5)
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = DHMQDGOQFOQNFH-UHFFFAOYSA-N
<!--| StdInChI2     = 1S/C2H5NO2.ClH/c3-1-2(4)5;/h1,3H2,(H,4,5);1H
| StdInChIKey2  = IVLXQGJVBGMLRR-UHFFFAOYSA-N -->
| CASNo = 56-40-6
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo2        = 6000-43-7
| CASNo2_Ref    = {{cascite|correct|CAS}}
| CASNo2_Comment = ([[Hydrochloride|HCl salt]])

| EC_number = 200-272-2
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 730
| ChemSpiderID2 = 20944
| PubChem = 750
| PubChem2      = 22316
| IUPHAR_ligand = 727
| DrugBank_Ref = {{drugbankcite|correct|drugbank}}
| DrugBank = DB00145
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 15428
| SMILES = C(C(=O)O)N 
| SMILES1 = C(C(=O)[O-])[NH3+] 
| SMILES1_Comment = [[Zwitterion]] 
| SMILES2       = C(C(=O)O)N.Cl
| EC_number2    = 227-841-8
}}
| Section2       = {{Chembox Properties
| C=2 | H=5 | N=1 | O=2
| Appearance = White solid
| Density = 1.1607 g/cm<sup>3</sup><ref>''Handbook of Chemistry and Physics'', CRC Press, 59th edition, 1978</ref>
| MeltingPtC = 233
| MeltingPt_notes = (decomposition)
| Solubility = 249.9 g/L (25 °C)<ref>{{Cite web |url=http://prowl.rockefeller.edu/aainfo/solub.htm |title=Solubilities and densities |publisher=Prowl.rockefeller.edu |access-date=2013-11-13 |archive-date=2017-09-12 |archive-url=https://web.archive.org/web/20170912101816/http://prowl.rockefeller.edu/aainfo/solub.htm |url-status=dead }}</ref>
| SolubleOther = soluble in [[pyridine]] <br/> sparingly soluble in [[ethanol]] <br/> insoluble in [[diethyl ether|ether]]
| pKa = 2.34 (carboxyl), 9.6 (amino)<ref>Dawson, R.M.C., et al., ''Data for Biochemical Research'', Oxford, Clarendon Press, 1959.</ref>
| MagSus = -40.3·10<sup>−6</sup> cm<sup>3</sup>/mol
  }}
| Section6       = {{Chembox Pharmacology
| ATCCode_prefix = B05
| ATCCode_suffix = CX03
}}
| Section7       = {{Chembox Hazards
| FlashPt =
| AutoignitionPt = 
| LD50 = 2600 mg/kg (mouse, oral)
  }}
}}

'''Glycine''' (symbol '''Gly''' or '''G''';<ref>{{Cite web |url=http://www.chem.qmul.ac.uk/iupac/AminoAcid/AA1n2.html |title=Nomenclature and Symbolism for Amino Acids and Peptides |year=1983 |publisher=IUPAC-IUB Joint Commission on Biochemical Nomenclature |url-status=dead |archive-url=https://web.archive.org/web/20081009023202/http://www.chem.qmul.ac.uk/iupac/AminoAcid/AA1n2.html |archive-date=9 October 2008 |access-date=5 March 2018}}</ref> {{IPAc-en|audio=En-us-Glycine.ogg||ˈ|ɡ|l|aɪ|s|iː|n}})<ref>{{Cite web |url=https://en.oxforddictionaries.com/definition/glycine |archive-url=https://web.archive.org/web/20180129004325/https://en.oxforddictionaries.com/definition/glycine |url-status=dead |archive-date=January 29, 2018 |title=Glycine &#124; Definition of glycine in English by Oxford Dictionaries}}</ref> is an [[amino acid]] that has a single [[hydrogen]] atom as its [[side chain]]. It is the simplest stable amino acid ([[carbamic acid]] is unstable).  Glycine is one of the [[proteinogenic amino acid]]s. It is [[Genetic code|encoded]] by all the [[codon]]s starting with GG (GGU, GGC, GGA, GGG).<ref name=":3">{{cite journal | vauthors = Pawlak K, Błażej P, Mackiewicz D, Mackiewicz P | title = The Influence of the Selection at the Amino Acid Level on Synonymous Codon Usage from the Viewpoint of Alternative Genetic Codes | journal = International Journal of Molecular Sciences | volume = 24 | issue = 2 | pages = 1185 | date = January 2023 | pmid = 36674703 | pmc = 9866869 | doi = 10.3390/ijms24021185 | doi-access = free }}</ref> Glycine is integral to the formation of [[Alpha helix|alpha-helices]] in [[secondary protein structure]] due to the [[Molecular geometry|"flexibility"]] caused by such a small R group. Glycine is also an inhibitory [[neurotransmitter]]<ref>{{cite journal | vauthors = Zafra F, Aragón C, Giménez C | title = Molecular biology of glycinergic neurotransmission | journal = Molecular Neurobiology | volume = 14 | issue = 3 | pages = 117–142 | date = June 1997 | pmid = 9294860 | doi = 10.1007/BF02740653 }}</ref> – interference with its release within the spinal cord (such as during a ''[[Clostridium tetani]]'' infection) can cause [[Spasticity|spastic]] paralysis due to uninhibited muscle contraction.<ref>{{Cite web |title=Comprehensive Toxicology |url=https://www.sciencedirect.com/referencework/9780081006016/comprehensive-toxicology |access-date=2024-10-18 |website=ScienceDirect |language=en}}</ref>

It is the only [[chirality (chemistry)|achiral]] [[proteinogenic amino acid]].<ref>{{cite journal | vauthors = Matsumoto A, Ozaki H, Tsuchiya S, Asahi T, Lahav M, Kawasaki T, Soai K | title = Achiral amino acid glycine acts as an origin of homochirality in asymmetric autocatalysis | journal = Organic & Biomolecular Chemistry | volume = 17 | issue = 17 | pages = 4200–4203 | date = April 2019 | pmid = 30932119 | doi = 10.1039/C9OB00345B }}</ref> It can fit into [[Hydrophile|hydrophilic]] or [[Hydrophobe|hydrophobic]] environments, due to its minimal side chain of only one hydrogen atom.<ref>{{cite journal | vauthors = Alves A, Bassot A, Bulteau AL, Pirola L, Morio B | title = Glycine Metabolism and Its Alterations in Obesity and Metabolic Diseases | journal = Nutrients | volume = 11 | issue = 6 | pages = 1356 | date = June 2019 | pmid = 31208147 | pmc = 6627940 | doi = 10.3390/nu11061356 | doi-access = free }}</ref>

==History and etymology==
Glycine was discovered in 1820 by French chemist [[Henri Braconnot]] when he hydrolyzed [[gelatin]] by boiling it with [[sulfuric acid]].<ref>{{Cite book | vauthors = Plimmer RH |url=https://books.google.com/books?id=7JM8AAAAIAAJ&pg=PA112 |title=The chemical composition of the proteins |publisher=Longmans, Green and Co. |year=1912 |edition=2nd |series=Monographs on biochemistry |volume=Part I. Analysis |location=London |page=82 |access-date=January 18, 2010 |orig-year=1908 | veditors = Plimmer RH, Hopkins F  }}</ref> He originally called it "sugar of gelatin",<ref>{{Cite journal | vauthors = Braconnot H |date=1820 |title=Sur la conversion des matières animales en nouvelles substances par le moyen de l'acide sulfurique |trans-title=On the conversion of animal materials into new substances by means of sulfuric acid |url=https://babel.hathitrust.org/cgi/pt?id=hvd.hx3dvk;view=1up;seq=119 |journal=Annales de Chimie et de Physique |series=2nd series |language=fr |volume=13 |pages=113–125}} ; see p. 114.</ref><ref>{{Cite book | vauthors = MacKenzie C |url=https://archive.org/details/onethousandexpe01mackgoog |title=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 … |date=1822 |publisher=Sir R. Phillips and Company |page=[https://archive.org/details/onethousandexpe01mackgoog/page/n650 557] |language=en}}</ref> but French chemist [[Jean-Baptiste Boussingault]] showed in 1838 that it contained nitrogen.<ref>{{Cite journal |last=Boussingault |date=1838 |title=Sur la composition du sucre de gélatine et de l'acide nitro-saccharique de Braconnot |trans-title=On the composition of sugar of gelatine and of nitro-glucaric acid of Braconnot |url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015035450702;view=1up;seq=515 |journal=Comptes Rendus |language=fr |volume=7 |pages=493–495}}</ref>  In 1847 American scientist [[Eben Norton Horsford]], then a student of the German chemist [[Justus von Liebig]], proposed the name "glycocoll";<ref>{{Cite journal | vauthors = Horsford EN |date=1847 |title=Glycocoll (gelatine sugar) and some of its products of decomposition |url=https://babel.hathitrust.org/cgi/pt?id=hvd.32044102902764;view=1up;seq=381 |journal=The American Journal of Science and Arts |series=2nd series |volume=3 |pages=369–381}}</ref><ref>{{Cite book | vauthors = Ihde AJ |url=https://books.google.com/books?id=89BIAwAAQBAJ&pg=PA167 |title=The Development of Modern Chemistry |date=1970 |publisher=Courier Corporation |isbn=9780486642352 |language=en}}</ref> however, the [[Sweden|Swedish]] chemist [[Jöns Jacob Berzelius|Berzelius]] suggested the simpler current name a year later.<ref>{{Cite book | vauthors = Berzelius J |url=https://books.google.com/books?id=mDc4AQAAIAAJ&q=%22glycin%22&pg=PA654 |title=Jahres-Bericht über die Fortschritte der Chemie und Mineralogie (Annual Report on the Progress of Chemistry and Mineralogy) |date=1848 |publisher=Laupp |volume=47 |location=Tübigen, (Germany) |page=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.)</ref><ref>{{Cite book | vauthors = Nye MJ |url= https://books.google.com/books?id=qKjxtZvnBKQC&pg=PA141 |title=Before Big Science: The Pursuit of Modern Chemistry and Physics, 1800-1940 |date=1999 |publisher=Harvard University Press |isbn=9780674063822 |language=en}}</ref> The name comes from the [[Ancient Greek|Greek]] word γλυκύς "sweet tasting"<ref>{{Cite web |url=http://oxforddictionaries.com/definition/american_english/glycine |archive-url=https://web.archive.org/web/20141113010813/http://www.oxforddictionaries.com/definition/american_english/glycine |url-status=dead |archive-date=November 13, 2014 |title=glycine |website=Oxford Dictionaries |access-date=2015-12-06}}</ref> (which is also related to the prefixes ''[[wikt:glyco-#Prefix|glyco-]]'' and ''[[wikt:gluco-#Prefix|gluco-]]'', as in ''[[glycoprotein]]'' and ''[[glucose]]'').  In 1858, the French chemist [[Auguste André Thomas Cahours|Auguste Cahours]] determined that glycine was an [[amine]] of [[acetic acid]].<ref>{{Cite journal | vauthors = Cahours A |date=1858 |title=Recherches sur les acides amidés |trans-title=Investigations into aminated acids |url=https://babel.hathitrust.org/cgi/pt?id=umn.31951d00008355e;view=1up;seq=1050 |journal=Comptes Rendus |language=fr |volume=46 |pages=1044–1047}}</ref>

==Production==

Although glycine can be isolated from [[hydrolyzed protein|hydrolyzed proteins]], this route is not used for industrial production, as it can be manufactured more conveniently by chemical synthesis.<ref>{{Cite book | vauthors = Okafor N  |url=https://books.google.com/books?id=PTm1CwAAQBAJ&pg=PA385 |title=Modern Industrial Microbiology and Biotechnology |date=2016-03-09 |publisher=CRC Press |isbn=9781439843239 |language=en}}</ref> The two main processes are [[amination]] of [[chloroacetic acid]] with [[ammonia]], giving glycine and [[ammonium chloride]],<ref>{{OrgSynth | vauthors = Ingersoll AW, Babcock SH | title = Hippuric acid | prep=cv2p0328 | volume = 12 | pages = 40 | year = 1932 | collvol = 2 | collvolpages = 328}}</ref> and the [[Strecker amino acid synthesis]],<ref>{{Cite book |url=https://books.google.com/books?id=f--1V1ftgtsC&pg=PA38 |title=Kirk-Othmer Food and Feed Technology, 2 Volume Set |date=2007-12-14 |publisher=John Wiley & Sons |isbn=9780470174487 |language=en}}</ref> which is the main synthetic method in the United States and Japan.<ref name="usitc.gov">{{Cite web |url=http://www.usitc.gov/trade_remedy/731_ad_701_cvd/investigations/2007/glycine_from_india_japan_korea/preliminary/DOC/Glycine%20Conference%20%28prelim%29.wpd |title=Glycine Conference (prelim) |publisher=USITC |url-status=bot: unknown |archive-url=https://web.archive.org/web/20120222063555/http://www.usitc.gov/trade_remedy/731_ad_701_cvd/investigations/2007/glycine_from_india_japan_korea/preliminary/DOC/Glycine%20Conference%20%28prelim%29.wpd |archive-date=2012-02-22 |access-date=2014-06-13}}</ref> About 15 thousand [[tonne]]s are produced annually in this way.<ref name="Ull">{{Ullmann| vauthors = Drauz KH, Grayson I, Kleemann A, Krimmer HP, Leuchtenberger W, Weckbecker C |year=2007|title=Amino Acids|doi10.1002/14356007.a02_057.pub2}}</ref>

Glycine is also co-generated as an impurity in the synthesis of [[EDTA]], arising from reactions of the ammonia co-product.<ref name="Ullmann/Roger">{{Ullmann| vauthors = Hart JR |year=2005|title=Ethylenediaminetetraacetic Acid and Related Chelating Agents|doi=10.1002/14356007.a10_095}}</ref>

==Chemical reactions==
Its acid–base properties are most important. In aqueous solution, glycine is [[amphoteric]]: below pH = 2.4, it converts to the ammonium cation called glycinium. Above about pH 9.6, it converts to glycinate.
:[[File:Glycine-protonation-states-2D-skeletal.png|540x540px]]

Glycine functions as a [[bidentate ligand]] for many metal ions, forming [[amino acid complex]]es.<ref>{{Cite journal | vauthors = Tomiyasu H, Gordon G |date=1976-04-01 |title=Ring closure in the reaction of metal chelates. Formation of the bidentate oxovanadium(IV)-glycine complex |url=https://pubs.acs.org/doi/abs/10.1021/ic50158a027 |journal=Inorganic Chemistry |language=en |volume=15 |issue=4 |pages=870–874 |doi=10.1021/ic50158a027 |issn=0020-1669}}</ref><ref>{{cite journal | vauthors = Mandado M, Cordeiro MN | title = On the stability of metal-aminoacid complexes in water based on water-ligand exchange reactions and electronic properties: detailed study on iron-glycine hexacoordinated complexes | journal = Journal of Computational Chemistry | volume = 31 | issue = 15 | pages = 2735–2745 | date = November 2010 | pmid = 20839300 | doi = 10.1002/jcc.21567 }}</ref> A typical complex is Cu(glycinate)<sub>2</sub>, i.e. Cu(H<sub>2</sub>NCH<sub>2</sub>CO<sub>2</sub>)<sub>2</sub>, which exists both in cis and trans isomers.<ref>{{cite journal | vauthors = Lutz OM, Messner CB, Hofer TS, Glätzle M, Huck CW, Bonn GK, Rode BM | title = Combined Ab Initio Computational and Infrared Spectroscopic Study of the cis- and trans-Bis(glycinato)copper(II) Complexes in Aqueous Environment | journal = The Journal of Physical Chemistry Letters | volume = 4 | issue = 9 | pages = 1502–1506 | date = May 2013 | pmid = 26282305 | doi = 10.1021/jz400288c }}</ref><ref>{{Cite journal | vauthors = D'Angelo P, Bottari E, Festa MR, Nolting HF, Pavel NV  |date= April 1998 |title=X-ray Absorption Study of Copper(II)−Glycinate Complexes in Aqueous Solution |journal=The Journal of Physical Chemistry B |language=en |volume=102 |issue=17 |pages=3114–3122 |doi=10.1021/jp973476m |issn=1520-6106}}</ref>

With acid chlorides, glycine converts to the amidocarboxylic acid, such as [[hippuric acid]]<ref>{{Cite journal | vauthors = Ingersoll AW, Babcock SH |year=1932 |title=Hippuric Acid |journal=Org. Synth. |volume=12 |page=40 |doi=10.15227/orgsyn.012.0040}}</ref> and [[acetylglycine]].<ref>{{Cite journal | vauthors = Herbst RM, Shemin D |year=1939 |title=Acetylglycine |journal=Org. Synth. |volume=19 |page=4 |doi=10.15227/orgsyn.019.0004}}</ref> With [[nitrous acid]], one obtains [[glycolic acid]] ([[van Slyke determination]]). With [[methyl iodide]], the amine becomes [[Quaternary compound|quaternized]] to give [[trimethylglycine]], a natural product:
:{{chem|H|3|N|+|CH|2|COO|-}} + 3 CH<sub>3</sub>I  →  {{chem|(CH|3|)|3|N|+|CH|2|COO|-}}  +  3 HI

Glycine condenses with itself to give peptides, beginning with the formation of [[glycylglycine]]<ref>{{cite journal | vauthors = Van Dornshuld E, Vergenz RA, Tschumper GS | title = Peptide bond formation via glycine condensation in the gas phase | journal = The Journal of Physical Chemistry. B | volume = 118 | issue = 29 | pages = 8583–8590 | date = July 2014 | pmid = 24992687 | doi = 10.1021/jp504924c }}</ref>:
:2 {{chem|H|3|N|+|CH|2|COO|-}}  →  {{chem|H|3|N|+|CH|2|CONHCH|2|COO|-}}  +  H<sub>2</sub>O
Pyrolysis of glycine or glycylglycine gives [[2,5-diketopiperazine]], the cyclic diamide.<ref>{{Cite journal | vauthors = Leng L, Yang L, Zu H, Yang J, Ai Z, Zhang W, Peng H, Zhan H, Li H, Zhong Q | date = November 2023 |title=Insights into glycine pyrolysis mechanisms: Integrated experimental and molecular dynamics/DFT simulation studies |journal=Fuel |volume=351 |pages=128949 |doi=10.1016/j.fuel.2023.128949 | bibcode = 2023Fuel..35128949L |issn=0016-2361}}</ref>

Glycine forms [[Ester|esters]] with [[Alcohol (chemistry)|alcohols]]. They are often isolated as their [[hydrochloride]], such as [[glycine methyl ester hydrochloride]]. Otherwise, the free ester tends to convert to [[diketopiperazine]].

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

==Metabolism==
===Biosynthesis===
Glycine is not [[Essential amino acid#Essentiality in humans|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]]. In most organisms, the enzyme [[serine hydroxymethyltransferase]] catalyses this transformation via the cofactor [[pyridoxal phosphate]]:<ref name="Lehninger" />
: serine + [[tetrahydrofolate]] → glycine + [[5,10-Methylenetetrahydrofolate|''N<sup>5</sup>'',''N<sup>10</sup>''-methylene tetrahydrofolate]] + H<sub>2</sub>O
In ''E. coli'', glycine is sensitive to antibiotics that target folate.<ref>{{cite journal | vauthors = Kwon YK, Higgins MB, Rabinowitz JD | title = Antifolate-induced depletion of intracellular glycine and purines inhibits thymineless death in E. coli | journal = ACS Chemical Biology | volume = 5 | issue = 8 | pages = 787–795 | date = August 2010 | pmid = 20553049 | pmc = 2945287 | doi = 10.1021/cb100096f }}</ref>

In the liver of [[vertebrate]]s, glycine synthesis is catalyzed by [[glycine synthase]] (also called glycine cleavage enzyme).  This conversion is readily [[Reversible reaction|reversible]]:<ref name="Lehninger" />
: CO<sub>2</sub> + NH{{su|b=4|p=+}} + ''N<sup>5</sup>'',''N<sup>10</sup>''-methylene tetrahydrofolate + [[Nicotinamide adenine dinucleotide|NADH]] + H<sup>+</sup> ⇌ Glycine + tetrahydrofolate + [[Nicotinamide adenine dinucleotide|NAD]]<sup>+</sup>

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.<ref>{{cite journal | vauthors = Wang W, Wu Z, Dai Z, Yang Y, Wang J, Wu G | title = Glycine metabolism in animals and humans: implications for nutrition and health | journal = Amino Acids | volume = 45 | issue = 3 | pages = 463–477 | date = September 2013 | pmid = 23615880 | doi = 10.1007/s00726-013-1493-1 | s2cid = 7577607 }}</ref>

===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]]:<ref name="Lehninger" />
: Glycine + tetrahydrofolate + NAD<sup>+</sup> ⇌ CO<sub>2</sub> + NH{{su|b=4|p=+}} + ''N<sup>5</sup>'',''N<sup>10</sup>''-methylene tetrahydrofolate + [[NADH]] + H<sup>+</sup>

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]].<ref name="Lehninger" />

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<sup>+</sup>-dependent reaction.<ref name="Lehninger" />

The half-life of glycine and its elimination from the body varies significantly based on dose.<ref name=":0" /> In one study, the half-life varied between 0.5 and 4.0 hours.<ref name=":0">{{cite journal | vauthors = Hahn RG | title = Dose-dependent half-life of glycine | journal = Urological Research | volume = 21 | issue = 4 | pages = 289–291 | year = 1993 | pmid = 8212419 | doi = 10.1007/BF00307714 | s2cid = 25138444 }}</ref>

==Physiological function==
The principal function of glycine is it acts as a [[Protein precursor|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]].<ref name="Lehninger">{{Lehninger4th|pages=127, 675–77, 844, 854}}</ref><ref name="SzpakJAS">{{Cite journal | vauthors = Szpak P |year=2011 |title=Fish bone chemistry and ultrastructure: implications for taphonomy and stable isotope analysis |url=https://uwo.academia.edu/PaulSzpak/Papers/827788/Fish_Bone_Chemistry_and_Ultrastructure_Implications_for_Taphonomy_and_Stable_Isotope_Analysis |journal=[[Journal of Archaeological Science]] |volume=38 |issue=12 |pages=3358–3372 |doi=10.1016/j.jas.2011.07.022|bibcode=2011JArSc..38.3358S }}</ref> In the [[genetic code]], glycine is coded by all [[codons]] starting with GG, namely GGU, GGC, GGA and GGG.<ref name=":3" />

===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 C<sub>2</sub>N subunit of all [[purine]]s.<ref name="Lehninger" />

===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 receptor]]s. In contrast to the inhibitory role of glycine in the spinal cord, this behaviour is facilitated at the ([[NMDA]]) [[glutamatergic]] receptors which are excitatory.<ref>{{Cite web |url=http://www.cmj.org/Periodical/paperlist.asp?id=LW7347&linkintype=pubmed |title=Recent development in NMDA receptors |year=2000 |publisher=Chinese Medical Journal}}</ref>  The {{LD50}} of glycine is 7930&nbsp;mg/kg in rats (oral),<ref>{{Cite web |url=http://physchem.ox.ac.uk/MSDS/GL/glycine.html |title=Safety (MSDS) data for glycine |year=2005 |publisher=The Physical and Theoretical Chemistry Laboratory Oxford University |url-status=dead |archive-url=https://web.archive.org/web/20071020054638/http://physchem.ox.ac.uk/MSDS/GL/glycine.html |archive-date=2007-10-20 |access-date=2006-11-01}}</ref> and it usually causes death by hyperexcitability.

=== As a toxin conjugation agent ===
Glycine [[Drug metabolism#Phase II – conjugation|conjugation]] pathway has not been fully investigated.<ref>{{cite journal | vauthors = van der Sluis R, Badenhorst CP, Erasmus E, van Dyk E, van der Westhuizen FH, van Dijk AA | title = Conservation of the coding regions of the glycine N-acyltransferase gene further suggests that glycine conjugation is an essential detoxification pathway | journal = Gene | volume = 571 | issue = 1 | pages = 126–134 | date = October 2015 | pmid = 26149650 | doi = 10.1016/j.gene.2015.06.081 }}</ref> Glycine is thought to be a hepatic detoxifier of a number endogenous and xenobiotic organic acids.<ref>{{cite journal | vauthors = Badenhorst CP, Erasmus E, van der Sluis R, Nortje C, van Dijk AA | title = A new perspective on the importance of glycine conjugation in the metabolism of aromatic acids | journal = Drug Metabolism Reviews | volume = 46 | issue = 3 | pages = 343–361 | date = August 2014 | pmid = 24754494 | doi = 10.3109/03602532.2014.908903 }}</ref> [[Bile acid]]s are normally conjugated to glycine in order to increase their solubility in water.<ref>{{cite journal | vauthors = Di Ciaula A, Garruti G, Lunardi Baccetto R, Molina-Molina E, Bonfrate L, Wang DQ, Portincasa P | title = Bile Acid Physiology | journal = Annals of Hepatology | volume = 16 | issue = Suppl. 1: s3-105 | pages = s4–s14 | date = November 2017 | pmid = 29080336 | doi = 10.5604/01.3001.0010.5493 | hdl-access = free | doi-access = free | hdl = 11586/203563 }}</ref>

The human body rapidly clears [[sodium benzoate]] by combining it with glycine to form [[hippuric acid]] which is then excreted.<ref>{{cite journal | vauthors = Nair B | title = Final report on the safety assessment of Benzyl Alcohol, Benzoic Acid, and Sodium Benzoate | journal = International Journal of Toxicology | volume = 20 Suppl 3 | issue = 3_suppl | pages = 23–50 | date = January 2001 | pmid = 11766131 | doi = 10.1080/10915810152630729 }}</ref> The metabolic pathway for this begins with the conversion of benzoate by [[butyrate-CoA ligase]] into an intermediate product, [[benzoyl-CoA]],<ref>{{cite web|title=butyrate-CoA ligase|url=https://www.brenda-enzymes.org/php/result_flat.php4?ecno=6.2.1.2&Suchword=&organism%5B%5D=Homo+sapiens&show_tm=0|work=BRENDA|publisher=Technische Universität Braunschweig.|access-date=7 May 2014}} Substrate/Product</ref> which is then metabolized by [[glycine N-acyltransferase|glycine ''N''-acyltransferase]] into hippuric acid.<ref>{{cite web|title=glycine N-acyltransferase|url=https://www.brenda-enzymes.org/php/result_flat.php4?ecno=2.3.1.13&Suchword=&organism%5B%5D=Homo+sapiens&show_tm=0|work=BRENDA|publisher=Technische Universität Braunschweig.|access-date=7 May 2014}} Substrate/Product</ref>

==Uses==
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.<ref>{{Cite web |url=http://www.usitc.gov/publications/701_731/pub3980.pdf |archive-url=https://web.archive.org/web/20100606111924/http://www.usitc.gov/publications/701_731/pub3980.pdf |archive-date=2010-06-06 |url-status=live |title=Glycine From Japan and Korea |date=January 2008 |publisher=U.S. International Trade Commission |access-date=2014-06-13}}</ref>

===Animal and human foods===
[[File:Cu(gly)2(OH2).png|thumb|Structure of ''cis''-Cu(glycinate)<sub>2</sub>(H<sub>2</sub>O)<ref>{{Cite journal | vauthors = Casari BM, Mahmoudkhani AH, Langer V |year=2004 |title=A Redetermination of ''cis''-Aquabis(glycinato-κ<sup>2</sup>''N,O'')copper(II) |journal=Acta Crystallogr. E |volume=60 |issue=12 |pages=m1949–m1951 |doi=10.1107/S1600536804030041}}</ref>]]
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.<ref name=Ull/>

{{As of|1971}}, the U.S. [[Food and Drug Administration]] "no longer regards glycine and its salts as [[generally recognized as safe]] for use in human food",<ref>{{Cite web |title=eCFR :: 21 CFR 170.50 -- Glycine (aminoacetic acid) in food for human consumption. |url=https://www.ecfr.gov/current/title-21/chapter-I/subchapter-B/part-170/subpart-C/section-170.50 |access-date=2022-10-24 |website=ecfr.gov}}</ref> and only permits food uses of glycine in certain conditions.<ref>{{Cite web |title=eCFR :: 21 CFR 172.812 -- Glycine |url=https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfCFR/CFRSearch.cfm?fr=172.812 |access-date=2024-07-06 |website=ecfr.gov}}</ref>

Glycine has been researched for its potential to [[Life extension|extend life]].<ref name=":2">{{cite journal | vauthors = Johnson AA, Cuellar TL | title = Glycine and aging: Evidence and mechanisms | journal = Ageing Research Reviews | volume = 87 | pages = 101922 | date = June 2023 | pmid = 37004845 | doi = 10.1016/j.arr.2023.101922 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Soh J, Raventhiran S, Lee JH, Lim ZX, Goh J, Kennedy BK, Maier AB | title = The effect of glycine administration on the characteristics of physiological systems in human adults: A systematic review | journal = GeroScience | volume = 46 | issue = 1 | pages = 219–239 | date = February 2024 | pmid = 37851316 | pmc = 10828290 | doi = 10.1007/s11357-023-00970-8 }}</ref> The proposed mechanisms of this effect are its ability to clear [[methionine]] from the body, and activating [[autophagy]].<ref name=":2" />

===Chemical feedstock===
Glycine is an intermediate in the synthesis of a variety of chemical products. It is used in the manufacture of the [[herbicide]]s [[glyphosate]],<ref>{{Cite book | vauthors = Stahl SS, Alsters PL |url=https://books.google.com/books?id=z5-tDAAAQBAJ&pg=PA268 |title=Liquid Phase Aerobic Oxidation Catalysis: Industrial Applications and Academic Perspectives |date=2016-07-13 |publisher=John Wiley & Sons |isbn=9783527690152 |language=en}}</ref> [[iprodione]], glyphosine, [[imiprothrin]], and eglinazine.<ref name=Ull/> It is used as an intermediate of [[antibiotic]]s such as [[thiamphenicol]].{{citation needed|date=July 2019}}

=== Laboratory research ===
Glycine is a significant component of some solutions used in the [[Polyacrylamide gel electrophoresis|SDS-PAGE]] method of protein analysis. It serves as a buffering agent, maintaining pH and preventing sample damage during electrophoresis.<ref>{{cite journal | vauthors = Schägger H | title = Tricine-SDS-PAGE | journal = Nature Protocols | volume = 1 | issue = 1 | pages = 16–22 | date = 2006-05-12 | pmid = 17406207 | doi = 10.1038/nprot.2006.4 }}</ref> 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.<ref>{{cite journal | vauthors = Legocki RP, Verma DP | title = Multiple immunoreplica Technique: screening for specific proteins with a series of different antibodies using one polyacrylamide gel | journal = Analytical Biochemistry | volume = 111 | issue = 2 | pages = 385–392 | date = March 1981 | pmid = 6166216 | doi = 10.1016/0003-2697(81)90577-7 }}</ref> 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 (spacecraft)|Stardust]]'' from comet [[Wild 2]] and subsequently returned to Earth. Glycine had previously been identified in the [[Murchison meteorite]] in 1970.<ref>{{cite journal | vauthors = Kvenvolden K, Lawless J, Pering K, Peterson E, Flores J, Ponnamperuma C, Kaplan IR, Moore C | title = Evidence for extraterrestrial amino-acids and hydrocarbons in the Murchison meteorite | journal = Nature | volume = 228 | issue = 5275 | pages = 923–926 | date = December 1970 | pmid = 5482102 | doi = 10.1038/228923a0 | bibcode = 1970Natur.228..923K | s2cid = 4147981 }}</ref> The discovery of glycine in outer space bolstered the hypothesis of so-called [[Pseudo-panspermia|soft-panspermia]], which claims that the "building blocks" of life are widespread throughout the universe.<ref>{{Cite news |url= https://www.reuters.com/article/scienceNews/idUSTRE57H02I20090818 |title=Building block of life found on comet - Thomson Reuters 2009 |date=18 August 2009 |access-date=2009-08-18 |work=Reuters}}</ref> In 2016, detection of glycine within Comet [[67P/Churyumov–Gerasimenko]] by the [[Rosetta (spacecraft)|''Rosetta'' spacecraft]] was announced.<ref>{{Cite news |author=European Space Agency |url=http://sci.esa.int/rosetta/57858-rosettas-comet-contains-ingredients-for-life/ |title=Rosetta's comet contains ingredients for life |date=27 May 2016 |access-date=2016-06-05}}</ref>

The detection of glycine outside the [[Solar System]] in the [[interstellar medium]] has been debated.<ref name="Snyder">{{cite journal | vauthors = Ramos MF, Silva NA, Muga NJ, Pinto AN | title = Reversal operator to compensate polarization random drifts in quantum communications | journal = Optics Express | volume = 28 | issue = 4 | pages = 5035–5049 | date = February 2020 | pmid = 32121732 | doi = 10.1086/426677 | bibcode = 2005ApJ...619..914S | arxiv = astro-ph/0410335 | s2cid = 16286204 }}</ref>

== Evolution ==
Glycine is proposed to be defined by early genetic codes.<ref>{{cite journal | vauthors = Trifonov EN | title = Consensus temporal order of amino acids and evolution of the triplet code | journal = Gene | volume = 261 | issue = 1 | pages = 139–151 | date = December 2000 | pmid = 11164045 | doi = 10.1016/S0378-1119(00)00476-5 }}</ref><ref>{{cite journal | vauthors = Higgs PG, Pudritz RE | title = A thermodynamic basis for prebiotic amino acid synthesis and the nature of the first genetic code | journal = Astrobiology | volume = 9 | issue = 5 | pages = 483–490 | date = June 2009 | pmid = 19566427 | doi = 10.1089/ast.2008.0280 | s2cid-access = free | arxiv = 0904.0402 | s2cid = 9039622 | bibcode = 2009AsBio...9..483H }}</ref><ref>{{cite journal | vauthors = Chaliotis A, Vlastaridis P, Mossialos D, Ibba M, Becker HD, Stathopoulos C, Amoutzias GD | title = The complex evolutionary history of aminoacyl-tRNA synthetases | journal = Nucleic Acids Research | volume = 45 | issue = 3 | pages = 1059–1068 | date = February 2017 | pmid = 28180287 | pmc = 5388404 | doi = 10.1093/nar/gkw1182 | doi-access = free }}</ref><ref name=":1">{{cite journal | vauthors = Ntountoumi C, Vlastaridis P, Mossialos D, Stathopoulos C, Iliopoulos I, Promponas V, Oliver SG, Amoutzias GD | title = Low complexity regions in the proteins of prokaryotes perform important functional roles and are highly conserved | journal = Nucleic Acids Research | volume = 47 | issue = 19 | pages = 9998–10009 | date = November 2019 | pmid = 31504783 | pmc = 6821194 | doi = 10.1093/nar/gkz730 | doi-access = free }}</ref> For example, [[Low complexity regions in proteins|low complexity regions]] (in proteins), that may resemble the proto-peptides of the early [[genetic code]] are highly enriched in glycine.<ref name=":1" />

==Presence in foods==
{|class=wikitable
|+ Food sources of glycine<ref>{{Cite web |title=FoodData Central Search Results for "Glycine (g)" |url=https://fdc.nal.usda.gov/fdc-app.html#/?component=1225 |access-date=2024-05-26 |website=fdc.nal.usda.gov}}</ref>
! Food
! Percentage<br>content<br>by weight<br>(g/100g)
|-
| Snacks, [[pork skins]] || 11.04
|-
| [[Sesame seed]]s 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 desserts || 1.96
|-
| Seeds, [[pumpkin]] and [[squash (plant)|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
|-
| [[Peanut]]s || 1.63
|-
| [[Crustacean]]s, spiny lobster || 1.59
|-
| Spices, [[mustard seed]], ground || 1.59
|-
| [[Salami]] || 1.55
|-
| Nuts, [[Juglans cinerea|butternuts]], dried || 1.51
|-
| Fish, salmon, pink, canned, drained solids || 1.42
|-
| [[Almond]]s || 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 ==
* [[Trimethylglycine]]
* [[Amino acid neurotransmitter]]

== References ==
{{Reflist}}

== Further reading ==
{{refbegin}}
* {{cite journal | vauthors = Nestler P, Helm CA | title = Determination of refractive index and layer thickness of nm-thin films via ellipsometry | journal = Optics Express | volume = 25 | issue = 22 | pages = 27077–27085 | date = October 2017 | pmid = 29092189 | doi = 10.1086/375637 | bibcode = 2003ApJ...593..848K | doi-access = free }}
*{{Cite web |url=https://www.newscientist.com/news/news.jsp?id=ns99992558 |title=Amino acid found in deep space | date = 18 July 2002 | work = New Scientist | vauthors = Nowak R |access-date=2007-07-01}}
* {{Cite journal | vauthors = Tsai GE |date=1 December 2008 |title=A New Class of Antipsychotic Drugs: Enhancing Neurotransmission Mediated by NMDA Receptors |url=http://www.psychiatrictimes.com/display/article/10168/1357569 |journal=Psychiatric Times |volume=25 |issue=14 |access-date=23 January 2009 |archive-date=3 October 2012 |archive-url=https://web.archive.org/web/20121003063816/http://www.psychiatrictimes.com/display/article/10168/1357569 |url-status=dead }}
* {{Cite journal |date=27 March 2008 |title=Organic Molecule, Amino Acid-Like, Found In Constellation Sagittarius |url=https://www.sciencedaily.com/releases/2008/03/080326161658.htm |journal=ScienceDaily}}
{{refend}}

== External links ==
{{Commons category}}
* [http://gmd.mpimp-golm.mpg.de/Spectrums/8a79d6c1-4849-4634-afe1-112d6e346bfb.aspx Glycine MS Spectrum]
* [https://en.longevitywiki.org/wiki/Glycine Glycine]
*[https://web.archive.org/web/20110511151841/http://www.chem.qmul.ac.uk/iubmb/enzyme/reaction/AminoAcid/GlyCleave.html Glycine cleavage system]
* [https://web.archive.org/web/20141221164448/http://www.schizophrenia.com/glycinetreat.htm Glycine Therapy - A New Direction for Schizophrenia Treatment?]
* [http://chemsub.online.fr/name/glycine.html ChemSub Online (Glycine)].
* [https://www.nasa.gov/mission_pages/stardust/news/stardust_amino_acid.html NASA scientists have discovered glycine, a fundamental building block of life, in samples of comet Wild 2 returned by NASA's Stardust spacecraft.]

{{Amino acids}}
{{Amino acid metabolism intermediates}}
{{Neurotransmitters}}
{{Glycine receptor modulators}}
{{Ionotropic glutamate receptor modulators}}
{{Molecules detected in outer space}}
{{Authority control}}

[[Category:Flavor enhancers]]
[[Category:Glucogenic amino acids]]
[[Category:Inhibitory amino acids]]
[[Category:Proteinogenic amino acids]]
[[Category:Glycine receptor agonists]]
[[Category:NMDA receptor agonists]]
[[Category:E-number additives]]
[[Category:Pages including recorded pronunciations]]