How is pepsin formed ?
Peptic and mucous cells in the stomach secrete pepsinogen. This pepsinogen has no digestive capability. As soon as it comes in contact with hydrochloric acid in the stomach it forms pepsin or gastric protease. If pepsin were secreted directly it would digest the protein in the cells that produced it. It’s active in a pH of 1.5 to 3.5. It has little activity in a pH above 5. Pepsin and hydrochloric acid are both necessary for protein digestion. If you don’t have enough hydrochloric acid the secreted pepsinogen can’t be turned to pepsin. Drugs such as histamine H2 receptor antagonists and proton pump inhibitors reduce stomach hydrochloric acid.