pepsin

A group of closely related aspartic proteinases. P. A is the principal digestive enzyme of gastric juice, formed from pepsinogen; it hydrolyzes peptide bonds at low pH values (is alkali-labile), preferably adjacent to phenylalanyl and leucyl residues, thus reducing proteins to smaller molecules (referred to as proteoses and peptones); p. B (gelatinase) is similar to p. A, but formed from porcine pepsinogen B and has a more restricted specificity; p. C (gastricsin is human p. C) is also similar to p. A, and structurally related to it, having a more restricted specificity. [G. pepsis, digestion]

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pep·sin 'pep-sən n

1) a crystallizable protease that in an acid medium digests most proteins to polypeptides (as by dissolving coagulated egg albumin or causing casein to precipitate from skim milk), that is secreted by glands in the mucous membrane of the stomach of higher animals, and that in combination with dilute hydrochloric acid is the chief active principle of gastric juice

2) a preparation containing pepsin obtained as a powder or scales from the stomach esp. of the hog and used esp. as a digestant

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n.

an enzyme in the stomach that begins the digestion of proteins by splitting them into peptones (see peptidase). It is produced by the action of hydrochloric acid on pepsinogen, which is secreted by the gastric glands. Once made, pepsin itself can act on pepsinogen to produce more pepsin.

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pep·sin (pepґsin) any of several enzymes of gastric juice that catalyze hydrolysis of proteins to form polypeptides.