Involved in the catabolism of arginine. Catalyzes the phosphorolysis of citrulline, the reverse reaction of the biosynthetic one, yielding ornithine and carbamoyl phosphate which serve to generate ATP from ADP. carbamoyl phosphate + L-ornithine = H(+) + L-citrulline + phosphate Ni(2+) ion bind each monomer of the trimer. Amino-acid degradation; L-arginine degradation via ADI pathway; carbamoyl phosphate from L-arginine: step 2/2. Homohexamer; dimer of trimers. The C-terminal end of the protein is critical for the stabilization of this oligomer. Belongs to the aspartate/ornithine carbamoyltransferase superfamily. OTCase family.