Catalyzes the second step of the urea cycle, the condensation of carbamoyl phosphate with L-ornithine to form L-citrulline (PubMed:14527149). The urea cycle ensures the detoxification of ammonia by converting it to urea for excretion (Probable). carbamoyl phosphate + L-ornithine = H(+) + L-citrulline + phosphate Negatively regulated by lysine acetylation. Nitrogen metabolism; urea cycle; L-citrulline from L-ornithine and carbamoyl phosphate: step 1/1. Homotrimer. Residues 88-96, 111-125 and 247-283 form flexible loops whose positions are affected on substrate binding. Acetylation at Lys-89 negatively regulates ornithine carbamoyltransferase activity in response to nutrient signals. Belongs to the aspartate/ornithine carbamoyltransferase superfamily. OTCase family.