The active site of the pepsin enzyme is obscured by a section of polypeptide (propeptide) chain - 44 amino acid residues long - and this is removed by the action of hydrochloric acid and pepsin already in the stomach. This means that the enzyme is inactive when first secreted from chief cells in the stomach wall, which prevents damage to the cells of the stomach wall itself.
Pepsinogen is converted by autocatalysis into the active form of the enzyme
pepsin.
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Secondary structure
Cartoon format - α helices red, β sheets gold
Active site
Aspartate residues 32, 215 in active site
Glycine residue 76 in flap above active site