pepsin

Examples of pepsin in the following topics:

• Denaturation and Protein Folding

  • Pepsin, the enzyme that breaks down protein in the stomach, only operates at a very low pH.
  • At higher pHs pepsin's conformation, the way its polypeptide chain is folded up in three dimensions, begins to change.
  • The stomach maintains a very low pH to ensure that pepsin continues to digest protein and does not denature.

• Hormones of the Digestive System

  • Gastrin is in the stomach and stimulates the gastric glands to secrete pepsinogen (an inactive form of the enzyme pepsin) and hydrochloric acid.
  • Motilin is in the duodenum and increases the migrating myoelectric complex component of gastrointestinal motility and stimulates the production of pepsin.

• Microscopic Anatomy of the Stomach

  • The cells at the base of these pits are chief cells, responsible for production of pepsinogen, an inactive precursor of pepsin, which degrades proteins.
  • The function of gastric acid is two fold: 1) it kills most of the bacteria in food, stimulates hunger, and activates pepsinogen into pepsin; and 2) it denatures the complex protein molecule as a precursor to protein digestion through enzyme action in the stomach and small intestines.

• Other Hormone-Producing Structures

  • Gastrin - is in the stomach and stimulates the gastric glands to secrete pepsinogen (an inactive form of the enzyme pepsin) and hydrochloric acid.
  • Motilin - is in the duodenum and increases the migrating myoelectric complex component of gastrointestinal motility and stimulates the production of pepsin.

• Mechanisms of Chemical Digestion

  • Stomach pepsin cleaves interior bonds of the amino acids, and is particularly important for its ability to digest collagen.
  • In the absence of stomach pepsin, digestion in the small intestine proceeds with difficulty.
  • Stomach pepsin digests about 20% of the proteins, the rest is digested by pancreatic and small intestine enzymes.

• Digestive System: Mouth and Stomach

  • Protein digestion is mediated in the stomach chamber by an enzyme called pepsin, which is secreted by the chief cells in the stomach in an inactive form called pepsinogen.
  • Hydrochloric acid helps to convert the inactive pepsinogen to pepsin.
  • The highly-acidic environment also kills many microorganisms in the food and, combined with the action of the enzyme pepsin, results in the hydrolysis of protein in the food.

• Gastric Phase

  • Below pH of two, stomach acid inhibits the parietal cells and G cells: a negative feedback loop that winds down the gastric phase as the need for pepsin and HCl declines.

• Chemical Digestion of Carbohydrates, Proteins, Lipids, and Nucleic Acids

  • Protein digestion occurs in the stomach and the duodenum through the action of three primary enzymes: pepsin, secreted by the stomach, and trypsin and chymotrypsin, secreted by the pancreas.

• Hydrolysis

  • Proteins are broken down by the enzymes trypsin, pepsin, peptidase and others.

• Digestive Properties of the Stomach

  • The biological effects of salivary EGF include healing of oral and gastroesophageal ulcers, inhibition of gastric acid secretion, and stimulation of DNA synthesis as well as mucosal protection from intraluminal injurious factors such as gastric acid, bile acids, pepsin, and trypsin, and to physical, chemical, and bacterial agents.