Responsible for initiating activation of pancreatic proteolytic proenzymes (trypsin, chymotrypsin and carboxypeptidase A). It catalyzes the conversion of trypsinogen to trypsin which in turn activates other proenzymes including chymotrypsinogen, procarboxypeptidases, and proelastases. Activation of trypsinogen by selective cleavage of 6-Lys-|-Ile-7 bond. Heterodimer of a catalytic (light) chain and a multidomain (heavy) chain linked by a disulfide bond. Intestinal brush border. The chains are derived from a single precursor that is cleaved by a trypsin-like protease. Belongs to the peptidase S1 family.