PEPSINOGEN SECRETION

Pepsinogen is released as a proenzyme (zymogen) from chief cells by exocytosis. The acidic gastric juice reversibly activates some pepsinogen molecules.

ACTIVATION OF PEPSINOGEN

These activated pepsinogen molecules then irreversibly activate themselves and the remaining inactive pepsinogen molecules by intramolecular and intermolecular cleavage to form pepsin. Catalysis removes an autoinhibitory domain (activation peptide) to expose the catalytic domain. This is an example of a positive feedback activation mechanism.