Proline

PROLINE (α-pyrrolidinecarboxylic acid), *

I a heterocyclic imino acid; D-proline is found among the products of hydrolysis of a protein molecule, in blood (traces), in fish meat, in the spleen of echinoderms, in germinated seeds; in significant quantities it is contained in prolamins, also in protamines, gelatin, and elastin. Proline crystallizes in the form of small needles, easily soluble in water and in alcohol. It has a sweetish taste. It decomposes at 215-220°; [α]d° = -79.8° to -80.9° (for a 4.4-6.5% aqueous solution). A solution of proline, acidified with sulfuric acid, is precipitated by phosphotungstic acid. During putrefaction, from D, L-proline, 5-aminovaleric acid and β-valeric acid are formed. Proline apparently has a relation to the synthesis of blood pigments in the organism. Besides proline, among the products of protein hydrolysis, L-oxiproline (γ-oxypyrrolidine-α-carboxylic acid) was also discovered, but-CH₂CH₂CH₂CH₂COOH, which is difficult to dissolve in absolute alcohol. It melts, decomposing, at 274°.