ornithine

An amino acid, C₅H₁₂N₂O₂, not found in proteins, formed by hydrolyzing arginine and important in the formation of urea.

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

an amino acid that does not occur in proteins but is important in the formation of urea