A zymogen (/
The pancreas secretes zymogens partly to prevent the enzymes from digesting proteins in the cells in which they are synthesised. Enzymes like pepsin are created in the form of pepsinogen, an inactive zymogen. Pepsinogen is activated when chief cells release it into the gastric acid, whose hydrochloric acid partially activates it. Another partially activated pepsinogen completes the activation by removing the peptide, turning the pepsinogen into pepsin. Accidental activation of zymogens can happen when the secretion duct in the pancreas is blocked by a gallstone resulting in acute pancreatitis.
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.
Another way that enzymes can exist in inactive forms and later be converted to active forms is by activating only when a cofactor, called a coenzyme, is bound. In this system, the inactive form (the apoenzyme) becomes the active form (the holoenzyme) when the coenzyme binds.
Examples of zymogens:
- Most proteins in the coagulation system (examples, prothrombin, or plasminogen)
- Some of the proteins of the complement system
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