Ornithine

Synonyms

Diaminovaleric acid

Definition

L-ornithine is a natural, biological, noncoded diamino acid (with α- and δ-amino groups). L-ornithine (Fig. 1) was first isolated by Jaffé from chicken excrement in 1877, hence its name (from Greek: oρνις (ornis) = bird). It plays a major role as a carrier compound in the metabolic urea cycle. Ornithine can be derived from glutamate and is used in the biosynthesis of arginine and is therefore indirectly coupled to protein synthesis in mammals. Polypeptides containing unprotected ornithines undergo spontaneous lactamization. L-ornithine is produced through hydrolysis of citrulline and L-arginine in alkaline medium, that is, the reverse of the biosynthetic process or the same direction observed in the urea cycle. Both L- and D-ornithine have been tentatively identified in the Murchison meteorites (Meierhenrich 2004) (concentration <5 ppb).

Fig. 1