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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.
The hydrolysis of a protein (red) by the nucleophilic attack of water (blue). The uncatalysed half-life is several hundred years. Proteolysis is the breakdown of proteins into smaller polypeptides or amino acids. Protein degradation is a major regulatory mechanism of gene expression [1] and contributes substantially to shaping mammalian ...
It is produced in the stomach by gastric chief cells in its inactive form pepsinogen, which is a zymogen. Pepsinogen is then activated by the stomach acid into its active form, pepsin. Pepsin breaks down the protein in the food into smaller particles, such as peptide fragments and amino acids.
The proenzyme Pepsinogen, with the exposure to hydrochloric acid gets converted into the active enzyme pepsin, the proteolytic enzyme of the stomach. Hydrochloric acid (HCl) provides the acidic pH (pH 1.8) optimal for pepsins. Rennin is a proteolytic enzyme found in gastric juice of infants which helps in the digestion of milk proteins.
The secretion is a complex and relatively energetically expensive process. Parietal cells contain an extensive secretory network (called canaliculi) from which the hydrochloric acid is secreted into the lumen of the stomach. The pH level is maintained by the proton pump H + /K + ATPase. [2]
When the chyme is exhausted of its nutrients the remaining waste material changes into the semi-solids called feces, which pass to the large intestine, where bacteria in the gut flora further break down residual proteins and starches. [32] Transit time through the small intestine is an average of 4 hours.
Chyme slowly passes through the pyloric sphincter and into the duodenum of the small intestine, where the extraction of nutrients begins. Gastric juice in the stomach also contains pepsinogen. Hydrochloric acid activates this inactive form of enzyme into the active form, pepsin. Pepsin breaks down proteins into polypeptides.
The gastric glands open into gastric pits in the mucosa. The gastric mucosa is covered in surface mucous cells that produce the mucus necessary to protect the stomach's epithelial lining from gastric acid secreted by parietal cells in the glands, and from pepsin, a secreted digestive enzyme. Surface mucous cells follow the indentations and ...