Pepsinogen is the inactive form of pepsin. Pepsinogen is a precursor to pepsin, which is an enzyme that breaks down proteins in your stomach. Pepsinogen exists in the stomach as well as in the cells lining the duodenum (the first section of the small intestine).

When you eat, food enters your stomach and mixes with a mixture of acids and digestive juices. One of these is hydrochloric acid (HCl). HCl has an important role in breaking down food into smaller particles for digestion.

Another digestive enzyme present in your stomach is pepsinogen. Pepsinogen starts out as proenzyme P1 (a part of the enzyme) and becomes active when it binds with HCl, forming P2. This makes pepsinogen a proenzyme. Once it binds with acid, it becomes a protease — an enzyme that breaks down proteins into smaller pieces called peptides and amino acids.

Last modified: October 28, 2022