Catalyzes the deimination of arginine residues of proteins. H2O + L-arginyl-[protein] = L-citrullyl-[protein] + NH4(+) Binding of Ca(2+) triggers a conformation change that is essential for catalytic activity. Homodimer. Spinal cord, submaxillary gland, cerebrum, cerebellum, and skeletal muscle. Belongs to the protein arginine deiminase family.