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|Section2={{Chembox Properties | C=2 | H=5 | N=1 | O=2 | MolarMass = 75.07 g/mol | Appearance = white solid | Density = 1.607 g/cm3 | MeltingPtC = 233 | MeltingPt_notes = (decomposition) | Solubility = 24.99 g/100 mL (25 °C) | SolubleOther = soluble in pyridine sparingly soluble in ethanol insoluble in ether | pKa = 2.34 (carboxyl), 9.6 (amino)Dawson, R.M.C., et al., Data for Biochemical Research, Oxford, Clarendon Press, 1959. | MagSus = -40.3·10−6 cm3/mol }} |Section6={{Chembox Pharmacology | ATCCode_prefix = B05 | ATCCode_suffix = CX03 }} |Section7={{Chembox Hazards | FlashPt = | AutoignitionPt = | LD50 = 2600 mg/kg (mouse, oral) }} }} Glycine (abbreviated as Gly or G) 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. 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.

History and etymology

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


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. The two main processes are amination of chloroacetic acid with ammonia, giving glycine and ammonium chloride, and the Strecker amino acid synthesis, which is the main synthetic method in the United States and Japan. About 15 thousand tonnes are produced annually in this way.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. Glycine is also cogenerated as an impurity in the synthesis of EDTA, arising from reactions of the ammonia coproduct.Hart, J. Roger (2005) "Ethylenediaminetetraacetic Acid and Related Chelating Agents" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim.

Acid-base properties

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. In most organisms, the enzyme serine hydroxymethyltransferase catalyses this transformation via the cofactor pyridoxal phosphate: 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: 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: 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. 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 varied between 0.5 and 4.0 hours.{{cite journal | author = Hahn RG | year = 1993 | title = Dose-dependent half-life of glycine | journal = Urological Research | volume = 21 | issue = 4 | pages = 289–291 | doi = 10.1007/BF00307714 | pmid = 8212419 }}

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

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 of glycine is 7930 mg/kg in rats (oral), 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.

Animal and human foods

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.

Cosmetics and miscellaneous applications

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. "Notice of Preliminary Determination of Sales at Less Than Fair Value: Glycine From India" Federal Register 72 (7 November 2007): 62827.

Chemical feedstock

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

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. 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 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.

See also


Further reading

External links

"green air" © 2007 - Ingo Malchow, Webdesign Neustrelitz
This article based upon the http://en.wikipedia.org/wiki/Glycine, the free encyclopaedia Wikipedia and is licensed under the GNU Free Documentation License.
Further informations available on the list of authors and history: http://en.wikipedia.org/w/index.php?title=Glycine&action=history
presented by: Ingo Malchow, Mirower Bogen 22, 17235 Neustrelitz, Germany