alanine ălˈənēnˌ [key], 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.

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