Catalyzes the deimination of arginine residues of proteins. H2O + L-arginyl-[protein] = L-citrullyl-[protein] + NH4(+) Monomer. Expressed only in the epidermis and uterus. Expressed during the estrus cycle. Expression is maximum at proestrus and moderate at estrus. Not expressed in diestrus and metaestrus phases. By estrogen. Belongs to the protein arginine deiminase family.