Extracellular zinc metalloprotease. Binds 4 Ca(2+) ions per subunit. Binds 1 zinc ion per subunit. Its casein hydrolytic activity is inhibited almost completely by a chelating agent (EDTA), whereas neither diisopropyl fluorophosphate nor phenylmethylsulfonyl fluoride inhibit the proteolytic activity in vitro. Optimum pH is about 7. Thermostable. Retains about 80% of its activity after treatment of 65 degrees Celsius for 30 minutes. Belongs to the peptidase M4 family.