Catalyzes the deimination of arginine residues of proteins. H2O + L-arginyl-[protein] = L-citrullyl-[protein] + NH4(+) Optimum temperature is 37 degrees Celsius. Found in wool follicles, keratinizing epithelia of the ruminal mucosa, embryonic hoof and tongue filiform papillae. The N-terminus is blocked. Belongs to the protein arginine deiminase family.