What Is Glycine?
Glycine is an amino acid with only hydrogen atoms in its side chain.
It is one of the 20 amino acids that make up proteins and is the only one of them that does not have a chiral carbon atom. It is abbreviated as Gly or G.
Glycine has a variety of functions and can be produced in the human body. It is particularly essential in the central nervous system and is present in high concentrations in the spinal cord and brain stem. It is a major amino acid in collagen and accounts for about one-third of the collagen in the body.
Uses of Glycine
Glycine has a chelating effect, making metals more soluble. This property can be used as a cleaning and polishing agent for precision instruments. It is an environmentally friendly chelating agent because it is easily decomposed by microorganisms. Glycine can be used in a variety of foods as a seasoning or as a means of improving shelf life.
Besides that, being the simplest amino acid, it is also used as a synthetic raw material for other amino acids. In addition to that, it can be used as a raw material for a wide variety of biological substances, such as collagen, porphyrins, glutathione, and creatine.
Properties of Glycine
Glycine is a white solid. It is soluble in ethanol and pyridine, but not in ether. It is soluble in water. The acid dissociation constant of the carboxyl group is pKa = 2.34 and that of the amino group is pKa = 9.6. It has a natural sweetness and excellent bacteriostatic properties that inhibit the action of bacteria.
Structure of Glycine
Glycine is 2-aminoacetic acid. It is also one of the 20 amino acids specified in the DNA of earth organisms. The side chain of the amino acid structure is a hydrogen atom (-H) and has no chiral carbon. Therefore, it is the only α-amino acid that has no stereoisomers (D-, L-) among the α-amino acids that make up living organisms.
The chemical formula is C2H5NO2 with a molar mass of 75.07 g/mol. Its specific formula is H2NCH2COOH and its density is 1.1607 g/cm3. Glycine is classified as a nonpolar side-chain amino acid. It is an amphoteric ion and dissociates on both the acidic and alkaline side. Specifically, it becomes an ammonium cation at pH = less than 2.4 and a glycinate at pH = greater than 9.6.
Other Information on Glycine
1. Biosynthesis and Metabolism of Glycine
The glycine cleavage system cleaves glycine by tetrahydrofolate to 5,10-methylenetetrahydrofolate. On the other hand, glycine can be reversibly interconverted to L-serine by the action of glycine hydroxymethyltransferase. The reaction is then catalyzed to convert 5,10-methylenetetrahydrofolate to tetrahydrofolate.
If glycine is deaminated, glycolic acid is formed, and oxidation yields glyoxylate. In humans, glyoxylate is an intermediate in the metabolism of ethylene glycol to oxalic acid. Oxidation produces oxalic acid, which is toxic. Metabolism of glycine is important to avoid oxidative reactions.
2. Reaction of Glycine
With acid chloride, glycine is converted to amide carboxylic acids such as horse uric acid and acetylglycine. With nitrite, glycine yields glycolic acid. In the reaction of glycine with methyl iodide, the amine is quaternized and the natural product trimethylglycine can be produced.
Besides, glycine can be condensed to form peptides. The first step is the formation of glycylglycine, a dipeptide of glycine. Other steps include the thermal decomposition of glycine and glycylglycine to yield 2,5-diketopiperazine, a cyclic diamide.
Glycine also forms esters with alcohols and can be isolated as glycine methyl ester hydrochloride. Furthermore, because of its amino and carboxy groups, it reacts with a variety of reagents as a bifunctional molecule.