alanine, organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer participates in the biosynthesis of proteins (see stereochemistry). Its side chain is a nonpolar, hydrophobic methyl group. The low reactivity of the amino acid permits silk, a protein which contains some 30% alanine, to have a simple, elongated structure with few cross-links. This contributes to the desirable features of the fiber-strength, resistance to stretching, and flexibility. Alanine is not essential to the human diet, since it can be synthesized from other cellular metabolites. It was discovered in protein in 1875.

Either of two organic compounds. Alpha-alanine is one of the nonessential amino acids, found in most proteins and particularly abundant in fibroin, the protein in silk. It is used in research and as a dietary supplement. Beta-alanine is a naturally occurring amino acid not found in proteins. It is an important constituent of the vitamin pantothenic acid and is used in its synthesis, as well as in biochemical research, electroplating, and organic synthesis.

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