H2O + L-arginine = L-citrulline + NH4(+) Amino-acid degradation; L-arginine degradation via ADI pathway; carbamoyl phosphate from L-arginine: step 1/2. Expression of arcA is significantly higher in cells that have entered stationary phase than in exponential-phase cells. Up-regulated by low pH and by arginine. Repressed by the CcpA protein. Part of the arc operon, that consists of the arcABCDT genes. Belongs to the arginine deiminase family.