Ornithine carbamoyltransferase involved in the synthesis of arginine from glutamate via ornithine and the urea cycle. carbamoyl phosphate + L-ornithine = H(+) + L-citrulline + phosphate Amino-acid biosynthesis; L-arginine biosynthesis; L-arginine from L-ornithine and carbamoyl phosphate: step 1/3. Interacts with trx2. Belongs to the aspartate/ornithine carbamoyltransferase superfamily. OTCase family.