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Pepsin / ˈ p ɛ p s ɪ n / is an endopeptidase that breaks down proteins into smaller peptides and amino acids. It is one of the main digestive enzymes in the digestive systems of humans and many other animals, where it helps digest the proteins in food. Pepsin is an aspartic protease, using a catalytic aspartate in its active site. [2]
Proteolysis in organisms serves many purposes; for example, digestive enzymes break down proteins in food to provide amino acids for the organism, while proteolytic processing of a polypeptide chain after its synthesis may be necessary for the production of an active protein.
Pepsin breaks down the protein in the food into smaller particles, such as peptide fragments and amino acids. Protein digestion, therefore, primarily starts in the stomach, unlike carbohydrate and lipids, which start their digestion in the mouth (however, trace amounts of the enzyme kallikrein , which catabolises certain protein, is found in ...
Water is a very minor source of hydrogen ions in comparison to carbonic acid. Carbonic acid is formed from carbon dioxide and water by carbonic anhydrase. The bicarbonate ion (HCO 3 −) is exchanged for a chloride ion (Cl −) on the basal side of the cell and the bicarbonate diffuses into the venous blood, leading to an alkaline tide phenomenon.
Ribbon diagram of a protease (TEV protease) complexed with its peptide substrate in black with catalytic residues in red.(. A protease (also called a peptidase, proteinase, or proteolytic enzyme) [1] is an enzyme that catalyzes proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the formation of new protein products. [2]
The enzyme is first made in the inactive form, pepsinogen by chief cells in the lining of the stomach. [24] With an impulse from the vagus nerve, pepsinogen is secreted into the stomach, where it mixes with hydrochloric acid to form pepsin. [25] Once active, pepsin works to break down proteins in foods such as dairy, meat, and eggs. [24]
The gastric chief cell (also known as a zymogenic cell or peptic cell) is a cell in the stomach that releases pepsinogen [1] and chymosin. Pepsinogen is activated into the digestive enzyme pepsin when it comes in contact with hydrochloric acid produced by gastric parietal cells. [2]
The parietal cell releases bicarbonate into the bloodstream in the process, which causes a temporary rise of pH in the blood, known as an alkaline tide. The acidic gastric juice also contains digestive enzymes produced by other cells in the gastric glands – gastric chief cells. Gastric chief cells secrete an inactivated pepsinogen.