Ornithine transcarbamylase (OTC) (also called ornithine carbamoyltransferase) is an enzyme (EC 2.1.3.3) that catalyzes the reaction between carbamoyl phosphate (CP) and ornithine (Orn) to form citrulline (Cit) and phosphate (Pi). There are two classes of OTC anabolic and catabolic. This article focuses on anabolic OTC. Anabolic OTC facilitates the sixth step in the biosynthesis of the amino acid arginine in prokaryotes.[5] In contrast, mammalian OTC plays an essential role in the urea cycle whose purpose is to capture toxic ammonia and transform it into less toxic urea nitrogen source for excretion.