Zymogen

A zymogen (or proenzyme) is an inactive enzyme precursor. A zymogen requires a biochemical change (such as a hydrolysis reaction revealing the active site, or changing the configuration to reveal the active site) for it to become an active enzyme. The biochemical change usually occurs in a lysosome where a specific part of the precursor enzyme is cleaved in order to activate it. The amino acid chain that is released upon activation is called the activation peptide.

The pancreas secretes zymogens partly to prevent the enzymes from digesting proteins in the cells in which they are synthesised. Fungi also secrete digestive enzymes into the environment as zymogens. The external environment has a different pH than inside the fungal cell and this changes the zymogen's structure into an active enzyme.

Examples
Examples of zymogens:


 * Angiotensinogen
 * Trypsinogen
 * Chymotrypsinogen
 * Pepsinogen
 * Most proteins in the coagulation system
 * Some of the proteins of the complement system
 * Caspases
 * Proelastase
 * Prolipase
 * Procarboxypolypeptidases