serine(redirected from Alternaria serine proteinase)
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serine (sĕrˈēn), organic compound, one of the 20 amino acids commonly found in animal proteins. Only the L-stereoisomer appears in mammalian protein. It is not essential to the human diet, since it can be synthesized in the body from other metabolites, including glycine. Serine is important in metabolism in that it participates in the biosynthesis of purines and pyrimidines, cysteine, tryptophan (in bacteria), and a large number of other metabolites. When incorporated into the structure of enzymes, serine often plays an important role in their catalytic function. It has been shown to occur in the active sites of chymotrypsin, trypsin, and many other enzymes. The so-called nerve gases and many substances used in insecticides have been shown to act by combining with a residue of serine in the active site of acetylcholine esterase, inhibiting the enzyme completely. Without the esterase activity that usually destroys acetylcholine as soon as it performs its function, dangerously high levels of this neurotransmitter build up, quickly resulting in convulsions and death. Serine was first obtained from silk protein, a particularly rich source, in 1865; its structure was established in 1902.
(also, α-amino-β-hydroxypropionic acid), HOCH2CH(NH2)COOH, a naturally occurring amino acid. Serine exists in two optically active forms, namely, the L and D forms, and in the racemic, or DL, form. Practically all proteins contain L-serine. The proteins of silk are especially rich in serine; fibroin contains up to 16 percent, and sericin up to <0 percent. Serine was isolated from sericin in 1865 by the German chemist E. Cramer. Phosphoesters of serine also enter into the composition of proteins. Serine is a replaceable amino acid; its precursor in biosynthesis by living organisms is D-3-phosphoglyceric acid, an intermediate product of glycolysis. In cells, serine participates in the biosynthesis of glycine, sulfur-containing amino acids (methionine, cysteine), and tryptophan, as well as of ethanolamine and sphingolipids. It serves as a source for a monocarbon fragment (conversion to glycine with the participation of tetrahydrofolic acid), which plays an important role in the biosynthesis of choline and purines:
Serine + Tetrahydrofolic acid → Glycine + N5, N10-methylene-tetrahydrofolic acid
Upon the decomposition of serine in organisms, pyruvic acid is formed, which is introduced into the tricarboxylic acid cycle by means of conversion into acetyl coenzyme A. The catalytic function of a series of enzymes (chymotrypsin, trypsin, bacterial proteases, esterases, phosphorylase, phosphoglucomutase, alkaline phosphatase) derives from the reactivity of the hy-droxyl group of the serine residue, which forms part of the active site of these enzymes. Reactions of the enzymes of the serine group include the hydrolysis of peptides, amides, and the esters of carboxylic acids and the transfer of the residue of phosphoric acid. The antibiotics cycloserine and azaserine are derivatives of serine.
REFERENCELehninger, A. Biokhimiia. Moscow, 1974. (Translated from English.)
E. N. SAFONOVA