Pepsin is one of the main protein degradation or proteolytic enzymes in the digestive system. During the digestion process, pepsin acts on complex dietary proteins and is broken down into peptides and amino acids that are easily absorbed by the intestinal wall. It can be used as an adjuvant treatment for anemia, especially in weight loss diets when protein intake increases. It is used as a research tool for protein analysis. It can also be used in tablets to increase appetite, and to prepare cheese and other protein-containing foods.
Pepsin is an aspartic protease and an endopeptidase that breaks down proteins into smaller peptides. Pepsin is one of the three main proteases in the human digestive system. Carbohydrates, fats and proteins are broken down in specific digestive enzymes and at specific locations in the digestive system. Pepsin is located in the stomach and plays a major role in protein breakdown. The digestion of protein by pepsin is not complete, and the digestive enzymes in the small intestine complete the work of breaking down food protein.
The stomach is a sack-like organ located in the upper left abdomen. It can hold up to 2 liters of food and liquids. When food enters the stomach, the strong muscles of the stomach wall stir the food and mix it with the gastric juice to produce “chyme.” Gastric juice contains mucus, hydrochloric acid and gastrin hormones, and stimulates the secretion of the precursor enzyme pepsinogen.
Pepsinogen is the precursor of pepsin, which is released by the main cells of the intestinal wall. Its primary structure consists of 44 amino acids. Compared with pepsin, pepsinogen is stable in neutral and weakly alkaline environments. The parietal cells of the stomach wall release hydrochloric acid, and pepsinogen can be activated by hydrochloric acid. When eating, gastrin and the vagus nerve trigger the gastric wall to release pepsinogen and hydrochloric acid. Hydrochloric acid creates an acidic environment, allowing pepsinogen to unfold and autocatalytically cleave, thereby producing pepsin.
The acid in the stomach causes food proteins to unfold in a process called denaturation. Denaturation exposes the molecular bonds of proteins so that pepsin can access them and break down the protein into smaller fragments called peptides or polypeptides. The small intestine continues to break down proteins by cutting peptides into amino acids, which are easily absorbed into the blood. Pepsin digests the protein for several hours and then slowly transfers the partially digested food mixture to the small intestine.
The mucus in the stomach protects the stomach wall from the potential damage of hydrochloric acid and pepsin. Stomach ulcer is a painful sore that may occur when the stomach wall is damaged. A bacterium called Helicobacter pylori can live in an acidic environment and is thought to prevent the secretion of protective mucus, which causes pepsin to form holes in the stomach wall. Antigastric drugs work by raising the pH in the stomach and inactivating pepsin, because pepsin only works at low pH. Long-term use of antacids is not recommended, because the inhibitory effect of pepsin will prevent adequate protein digestion. Absorption of incompletely digested protein fragments may cause allergies and other health problems.