A group of closely related aspartic proteinases. Pepsin 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); pepsin B (gelatinase) is similar to pepsin A, but formed from porcine pepsinogen B and has a more restricted specificity; pepsin C (gastricsin is human pepsin C) is also similar to pepsin A, and structurally related to it, having a more restricted specificity.
[G. pepsis, digestion]
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Examples: glitazone, GI cocktail, etc.