Reversibly catalyzes the transfer of the carbamoyl group from carbamoyl phosphate (CP) to the N(epsilon) atom of ornithine (ORN) to produce L-citrulline. carbamoyl phosphate + L-ornithine = H(+) + L-citrulline + phosphate Arginine lead to a slight activation. Inhibited by all nucleotide phosphates. Optimum pH is 8.8. At the physiological pH of 7, activity is only about 30%. Amino-acid degradation; L-arginine degradation via ADI pathway; carbamoyl phosphate from L-arginine: step 2/2. Homohexamer. Not stable below 1 M KCl. Belongs to the aspartate/ornithine carbamoyltransferase superfamily. OTCase family.