Glycine

Glycine (symbol Gly or G; /ˈɡlaɪsiːn/) 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 formula NH2‐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 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 (symbol Gly or G; /ˈɡlaɪsiːn/) 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 formula NH2‐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 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 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 was discovered in 1820 by the French chemist Henri Braconnot when he hydrolyzed gelatin by boiling it with sulfuric acid. He originally called it 'sugar of gelatin', but the French chemist Jean-Baptiste Boussingault showed that it contained nitrogen. The American scientist Eben Norton Horsford, then a student of the German chemist Justus von Liebig, proposed the name 'glycocoll'; however, the Swedish chemist Berzelius suggested the simpler name 'glycine'. The name comes from the Greek word γλυκύς 'sweet tasting' (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. 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. Glycine is also cogenerated as an impurity in the synthesis of EDTA, arising from reactions of the ammonia coproduct. 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.