The Pepsinogen molecule - rotatable in 3 dimensions

Pepsinogen is the inactive version - also called a pro-enzyme, zymogen or precursor - of pepsin, a protease (protein-digesting enzyme), secreted in the stomach.

The porcine pepsinogen molecule displayed here consists of 370 amino acid residues - 3031 atoms, ignoring hydrogen atoms, but this also includes oxygens from 237 water molecules!

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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Show 44 extra amino acids of propeptide
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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