Selectively cleaves synthetic peptide substrates of trypsin. Activates the epithelial sodium channel ENaC. Inhibited by aprotinin, leupeptin, benzamidine and soybean trypsin inhibitor. Partially inhibited by PMSF and DFP. Optimum pH is 9.0. Expressed predominantly in kidney, small intestine and stomach and moderately in thymus, lung, spleen, testis and skin. In the kidney, expressed mainly in collecting duct of renal medulla and cortex. By aldosterone. Belongs to the peptidase S1 family.