Catalyzes the deimination of arginine residues of proteins. H2O + L-arginyl-[protein] = L-citrullyl-[protein] + NH4(+) Epidermis and hair follicles. No visible phenotype. The skin of 7-week-old null mice appeared normal, but scanning electron microscopy revealed structural alterations in the whiskers and hair coat morphology (PubMed:27866708). Belongs to the protein arginine deiminase family.