Localized to zymogen granules, where it functions in trypsinogen activation (PubMed:12401800). May indirectly regulate cell motility, cell-cell and cell/extracellular matrix interactions (By similarity). Highly expressed in pancreatic acinar cells. Also expressed in epithelium of the uterus during late pregnancy but not detected in non-pregnant uterus or in a variety of other adult and fetal tissues. First detected in uterus 6 days prior to birth, increases daily to reach maximum levels 3 days before birth, abruptly decreases during the last 3 days of pregnancy and is almost undetectable by the first day after birth. Mice display increased severity of secretagogue- and diet-induced pancreatitis which seems to be due to impaired activation of trypsin.