Glycine

Source: Wikipedia, the free encyclopedia.
For other uses, see Glycine (disambiguation).
Not to be confused with
Glycerin
.

Glycine[1]
Skeletal formula of neutral glycine
Skeletal formula of zwitterionic glycine
Ball-and-stick model of the gas-phase structure
Ball-and-stick model of the zwitterionic solid-state structure
Space-filling model of the gas-phase structure
Space-filling model of the zwitterionic solid-state structure
Names
IUPAC name
Glycine
Systematic IUPAC name
Aminoacetic acid[2]
Other names
  • 2-Aminoethanoic acid
  • Glycocol
  • Glycic acid
  • Dicarbamic acid
Identifiers
3D model (
JSmol
)
Abbreviations Gly, G
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard
 100.000.248 Edit this at Wikidata
EC Number
  • 200-272-2
  • (HCl): 227-841-8
IUPHAR/BPS
KEGG
UNII
  • InChI=1S/C2H5NH2/c3-1-2(4)5/h1,3H2,(H,4,5) checkY
    Key: DHMQDGOQFOQNFH-UHFFFAOYSA-N checkY
  • InChI=1S/C2H5NO2/c3-1-2(4)5/h1,3H2,(H,4,5)
    Key: DHMQDGOQFOQNFH-UHFFFAOYAW
Properties
C2H5NO2
Molar mass 75.067 g·mol−1
Appearance White solid
Density 1.1607 g/cm3[3]
Melting point 233 °C (451 °F; 506 K) (decomposition)
249.9 g/L (25 °C)[4]
Solubility soluble in pyridine
sparingly soluble in ethanol
insoluble in ether
Acidity (pKa) 2.34 (carboxyl), 9.6 (amino)[5]
-40.3·10−6 cm3/mol
Pharmacology
B05CX03 (WHO)
Hazards
Lethal dose or concentration (LD, LC):
2600 mg/kg (mouse, oral)
Supplementary data page
Glycine (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Glycine (symbol Gly or G;

secondary protein structure due to the "flexibility" caused by such a small R group. 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.

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.

History and etymology

Glycine was discovered in 1820 by French chemist Henri Braconnot when he hydrolyzed gelatin by boiling it with sulfuric acid.[8] He originally called it "sugar of gelatin",[9][10] but French chemist Jean-Baptiste Boussingault showed in 1838 that it contained nitrogen.[11] In 1847 American scientist Eben Norton Horsford, then a student of the German chemist Justus von Liebig, proposed the name "glycocoll";[12][13] however, the Swedish chemist Berzelius suggested the simpler current name a year later.[14][15] The name comes from the Greek word γλυκύς "sweet tasting"[16] (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.[17]

Production

Although glycine can be isolated from hydrolyzed protein, this route is not used for industrial production, as it can be manufactured more conveniently by chemical synthesis.[18] The two main processes are amination of chloroacetic acid with ammonia, giving glycine and ammonium chloride,[19] and the Strecker amino acid synthesis,[20] which is the main synthetic method in the United States and Japan.[21] About 15 thousand tonnes are produced annually in this way.[22]

Glycine is also cogenerated as an impurity in the synthesis of

EDTA, arising from reactions of the ammonia coproduct.[23]

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 9.6, it converts to glycinate.

Glycine functions as a

amino acid complexes
. A typical complex is Cu(glycinate)2, i.e. Cu(H2NCH2CO2)2, which exists both in cis and trans isomers.

With acid chlorides, glycine converts to the amidocarboxylic acid, such as

methyl iodide, the amine becomes quaternized to give trimethylglycine
, 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.

It forms esters with alcohols. They are often isolated as their hydrochloride, e.g., 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

3-phosphoglycerate, but one publication made by supplements sellers seems to show that the metabolic capacity for glycine biosynthesis does not satisfy the need for collagen synthesis.[26] In most organisms, the enzyme serine hydroxymethyltransferase catalyses this transformation via the cofactor pyridoxal phosphate:[27]

serine +
tetrahydrofolate → glycine + N5,N10-methylene tetrahydrofolate
+ H2O

In E. coli, glycine is sensitive to antibiotics that target folate.[28]

In the liver of

glycine synthase (also called glycine cleavage enzyme). This conversion is readily reversible:[27]

CO2 + NH+
4 + N5,N10-methylene tetrahydrofolate + NADH + H+ ⇌ Glycine + tetrahydrofolate + NAD+

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.[29]

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:[27]

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.[27]

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.[27]

The half-life of glycine and its elimination from the body varies significantly based on dose.[30] In one study, the half-life varied between 0.5 and 4.0 hours.[30]

Physiological function

The principal function of glycine is it acts as a

codons
starting with GG, namely GGU, GGC, GGA and GGG.

As a biosynthetic intermediate

In higher

ALA synthase. Glycine provides the central C2N subunit of all purines.[27]

As a neurotransmitter

Glycine is an inhibitory

NMDA) glutamatergic receptors which are excitatory.[32] The LD50 of glycine is 7930 mg/kg in rats (oral),[33]
and it usually causes death by hyperexcitability.

As a toxin conjugation agent

Glycine conjugation pathway has not been fully investigated.[34] Glycine is thought to be a hepatic detoxifier of a number endogenous and xenobiotic organic acids.[35] Bile acids are normally conjugated to glycine in order to increase their solubility in water.[36]

The human body rapidly clears sodium benzoate by combining it with glycine to form

butyrate-CoA ligase into an intermediate product, benzoyl-CoA,[38] which is then metabolized by glycine N-acyltransferase into hippuric acid.[39]

Uses

In the US, glycine is typically sold in two grades:

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.[40]

Animal and human foods

Structure of cis-Cu(glycinate)2(H2O)[41]

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.[22]

The U.S. "Food and Drug Administration no longer regards glycine and its salts as generally recognized as safe for use in human food".[42]

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,[43] iprodione, glyphosine, imiprothrin, and eglinazine.[22] It is used as an intermediate of antibiotics 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

Wild 2 and subsequently returned to Earth. Glycine had previously been identified in the Murchison meteorite in 1970.[44] The discovery of glycine in outer space bolstered the hypothesis of so called soft-panspermia, which claims that the "building blocks" of life are widespread throughout the universe.[45] In 2016, detection of glycine within Comet 67P/Churyumov–Gerasimenko by the Rosetta spacecraft was announced.[46]

The detection of glycine outside the Solar System in the interstellar medium has been debated.[47]

Evolution

Glycine is proposed to be defined by early genetic codes.[48][49][50][51] For example, low complexity regions (in proteins), that may resemble the proto-peptides of the early genetic code are highly enriched in glycine.[51]

Presence in foods

Food sources of glycine[52]
Food Percentage
content
by weight
(g/100g)
Snacks,
pork skins
 11.04
Sesame seeds
flour (low fat)		 3.43
Beverages,
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,
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

References

  1. ISBN 091191028X
    , 4386
  2. ^ pubchem.ncbi.nlm.nih.gov/compound/750#section=IUPAC-Name&fullscreen=true
  3. ^ Handbook of Chemistry and Physics, CRC Press, 59th edition, 1978
  4. ^ "Solubilities and densities". Prowl.rockefeller.edu. Archived from the original on September 12, 2017. Retrieved November 13, 2013.
  5. ^ Dawson, R.M.C., et al., Data for Biochemical Research, Oxford, Clarendon Press, 1959.
  6. ^ "Nomenclature and Symbolism for Amino Acids and Peptides". IUPAC-IUB Joint Commission on Biochemical Nomenclature. 1983. Archived from the original on October 9, 2008. Retrieved March 5, 2018.
  7. ^ "Glycine | Definition of glycine in English by Oxford Dictionaries". Archived from the original on January 29, 2018.
  8. ^ Plimmer, R.H.A. (1912) [1908]. Plimmer, R.H.A.; Hopkins, F.G. (eds.). The chemical composition of the proteins. Monographs on biochemistry. Vol. Part I. Analysis (2nd ed.). London: Longmans, Green and Co. p. 82. Retrieved January 18, 2010.
  9. ^ 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.
  10. ^ 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.
  11. ^ 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.
  12. ^ 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.
  13. ISBN 9780486642352
    .
  14. ^ 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.)
  15. ISBN 9780674063822
    .
  16. ^ "glycine". Oxford Dictionaries. Archived from the original on November 13, 2014. Retrieved December 6, 2015.
  17. ^ Cahours, A. (1858). "Recherches sur les acides amidés" [Investigations into aminated acids]. Comptes Rendus (in French). 46: 1044–1047.
  18. ISBN 9781439843239
    .
  19. ^ Ingersoll, A. W.; Babcock, S. H. (1932). "Hippuric acid". Organic Syntheses. 12: 40; Collected Volumes, vol. 2, p. 328.
  20. ISBN 9780470174487
    .
  21. ^ "Glycine Conference (prelim)". USITC. Archived from the original on February 22, 2012. Retrieved June 13, 2014.{{cite web}}: CS1 maint: bot: original URL status unknown (link)
  22. ^
    ISBN 978-3527306732
    .
  23. ISBN 978-3527306732
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  24. doi:10.15227/orgsyn.012.0040
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  25. doi:10.15227/orgsyn.019.0004
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  26. S2CID 2786988
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  27. ^
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  28. PMID 20553049
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  29. S2CID 7577607
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  31. doi:10.1016/j.jas.2011.07.022
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  32. ^ "Recent development in NMDA receptors". Chinese Medical Journal. 2000.
  33. ^ "Safety (MSDS) data for glycine". The Physical and Theoretical Chemistry Laboratory Oxford University. 2005. Archived from the original on October 20, 2007. Retrieved November 1, 2006.
  34. PMID 26149650
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  37. ISSN 1091-5818
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  38. ^ "butyrate-CoA ligase". BRENDA. Technische Universität Braunschweig. Retrieved May 7, 2014. Substrate/Product
  39. ^ "glycine N-acyltransferase". BRENDA. Technische Universität Braunschweig. Retrieved May 7, 2014. Substrate/Product
  40. ^ "Glycine From Japan and Korea" (PDF). U.S. International Trade Commission. January 2008. Archived (PDF) from the original on June 6, 2010. Retrieved June 13, 2014.
  41. doi:10.1107/S1600536804030041
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  42. ^ "eCFR :: 21 CFR 170.50 -- Glycine (aminoacetic acid) in food for human consumption". ecfr.gov. Retrieved October 24, 2022.
  43. ISBN 9783527690152
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  44. S2CID 4147981
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  45. ^ "Building block of life found on comet - Thomson Reuters 2009". Reuters. August 18, 2009. Retrieved August 18, 2009.
  46. ^ European Space Agency (May 27, 2016). "Rosetta's comet contains ingredients for life". Retrieved June 5, 2016.
  47. S2CID 16286204
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  48. PMID 11164045
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  51. ^
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  52. ^ "National Nutrient Database for Standard Reference". U.S. Department of Agriculture. Archived from the original on March 3, 2015. Retrieved September 7, 2009.

Further reading

External links

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