carbamoyl phosphate + L-ornithine = H(+) + L-citrulline + phosphate Amino-acid degradation; L-arginine degradation via ADI pathway; carbamoyl phosphate from L-arginine: step 2/2. Probably nonameric or dodecameric. Belongs to the aspartate/ornithine carbamoyltransferase superfamily. OTCase family.