Digestive protease that cleaves proteins preferentially after an Arg residue and has proteolytic activity toward Kunitz-type trypsin inhibitors. Preferential cleavage: Arg-|-Xaa, Lys-|-Xaa. Binds 1 Ca(2+) ion per subunit. Not inhibited by Kunitz-type trypsin inhibitors. Optimum pH is 8.5. Detected in pancreas and pancreatic fluid (at protein level) (PubMed:6698368). Expressed in pancreas and brain (PubMed:8294000). Detected in ileum (PubMed:12021776). Belongs to the peptidase S1 family.