Pepsin (redirected from Peptin)

pepsin, enzyme produced in the mucosal lining of the stomach that acts to degrade protein. Pepsin is one of three principal protein-degrading, or proteolytic, enzymes in the digestive system, the other two being chymotrypsin and trypsin. The three enzymes were among the first to be isolated in crystalline form. During the process of digestion, these enzymes, each of which is particularly effective in severing links between particular types of amino acids, collaborate to break down dietary proteins to their components, i.e., peptides and amino acids, which can be readily absorbed by the intestinal lining. In the laboratory studies pepsin is most efficient in cleaving bonds involving the aromatic amino acids, phenylalanine, tryptophan, and tyrosine. Pepsin is synthesized in an inactive form by the stomach lining; hydrochloric acid, also produced by the gastric mucosa, is necessary to convert the inactive enzyme and to maintain the optimum acidity (pH 1–3) for pepsin function. Pepsin and other proteolytic enzymes are used in the laboratory analysis of various proteins; pepsin is also used in the preparation of cheese and other protein-containing foods.

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pepsin

Powerful enzyme in gastric juice (see stomach) that partially digests proteins in food. Glands in the stomach lining make pepsinogen, a zymogen (enzyme precursor) converted to pepsin by the hydrochloric acid in gastric juice. Pepsin is active only in the acid environment of the stomach (pH 1.5–2.5 or less); it is ineffective in the intestine (pH 7, neutral). It is used commercially in some cheese making, in the leather industry to remove hair and residual tissue from hides, and in the recovery of silver from discarded photographic films by digesting the gelatin layer that holds the silver.

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pepsin, pepsine

a proteolytic enzyme produced in the stomach in the inactive form pepsinogen, which, when activated by acid, splits proteins into peptones

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pepsin [′pep·sən]

(biochemistry)

A proteolytic enzyme found in the gastric juice of mammals, birds, reptiles, and fishes.

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Pepsin 

a proteolytic enzyme of the hydrolase class, found in the gastric juice of mammals, birds, reptiles, and most species of fish. Pepsin breaks down proteins and peptides. It was first recognized in 1836 by T. Schwann and isolated in crystal form in 1930 by J. Northrop.

Pepsin is a globular protein with a molecular weight of approximately 34,500. A pepsin molecule is a polypeptide chain consisting of 340 amino-acid residues, three disulfide bonds (—S—S—), and phosphoric acid. The isoelectric point of pepsin is approximately equal to pH 1.0. Therefore, pepsin is stable in a strongly acid medium and reaches its maximum activity at pH 1–2, the pH of gastric juice. It undergoes denaturation at pH 6.0.

Pepsin is an endopeptidase, that is, an enzyme that splits the central peptide bonds in protein and peptide molecules, except keratins and other scleroproteins, to form simpler peptides and free amino acids. It very rapidly hydrolyzes peptide bonds formed by the aromatic amino acids tyrosine and phenylalanine; however, unlike the proteolytic enzymes trypsin and chymotrypsin, it does not exhibit a strong specificity.

Pepsin is produced by the gastric chief cells in the form of inactive pepsinogen. Pepsinogen is then converted to pepsin by the splitting off of several peptides, including a pepsin inhibitor, from the N-terminal section of pepsinogen. The activation process involves several stages and is catalyzed by the hydrochloric acid in gastric juice and by pepsin itself (autocatalysis).

Pepsin is used in the laboratory investigation of the primary structure of proteins, in cheese-making, and in the treatment of certain gastrointestinal diseases.

N. N. ZAITSEVA