Ornithine transcarbamylase
![](/Images/godic/202501/31/Ornithine_carbamoyltransferase_trimer_1OTH0543.png"){kind=spacer}
![](/Images/godic/202501/31/PBB_GE_OTC_207200_at_tn0543.png")
![The reaction mechanism of OTC.The side-chain amino group of Orn attacks the carbonyl carbon of CP nucleophilically, left, to form a tetrahedral transition state, middle. Charge rearrangement releases Cit and Pi, right.[1]](/Images/godic/202501/31/OTC_reaction0543.png")
![OTC monomer](/Images/godic/202501/31/OTC_structure0543.png")
Ornithine transcarbamylase (OTC) (also called ornithine carbamoyltransferase) is an enzyme that catalyzes the reaction between carbamoyl phosphate (CP) and ornithine (Orn) to form citrulline (Cit) and phosphate (Pi). In plants and microbes, OTC is involved in arginine (Arg) biosynthesis, whereas in mammals it is located in the mitochondria and is part of the urea cycle.