(biochemistry, organic chemistry) An amino acid, 2,5-diaminopentanoic acid, that is not present in protein, but is an intermediate in the biosynthesis of urea.

plural of ornithine

(biochemistry) An enzyme that catalyzes the reaction between carbamoyl phosphate and ornithine to form citrulline and phosphate.

(biochemistry) The enzyme ornithine transcarbamylase.

(biochemistry) The urea cycle.

(pathology) A rare genetic metabolic disorder of the urea cycle. Abbreviated as OTC.