Hydrochloric acid creates an acidic environment, which allows pepsinogen to unfold and cleave itself in an autocatalytic fashion, thereby generating pepsin (the active form). Pepsin cleaves the 44 amino acids from pepsinogen to create more pepsin.

How does HCl interact with pepsinogen?

HCl also converts pepsinogen to the active enzyme pepsin. Pepsin is a protease, meaning that it cleaves bonds in proteins. It breaks down the proteins in food into individual peptides (shorter segments of amino acids). The other enzyme that is active in the stomach is gastric lipase.

How does acid affect pepsinogen?

Chief cells are also the cellular source of pepsinogen, the inactive precursor of pepsin. On secretion and exposure to stomach acid, inactive pepsinogen undergoes a conformational change, exposing its catalytically active site. This now-active form of pepsinogen generates pepsin from inactive pepsinogen by proteolysis.