Zymogen

A zymogen (from the Greek zymē - leaven, fermentation and gennan - to give birth) or proenzyme is an inactive form of an enzyme that is converted into an active form as a result of limited proteolysis or other chemical changes.

Zymogens are synthesized in an inactive form to prevent unwanted proteolysis in the cell. Activation of zymogens occurs in the right place and at the right time, for example, in the gastrointestinal tract or in lysosomes.

Examples of zymogens: pepsinogen, which is converted to active pepsin in the acidic environment of the stomach; trypsinogen, activated by enterokinase in the intestine; proinsulin, which is converted to insulin.

The activated form of zymogen is called zymase. Zymogen and zymase differ in conformation, which determines their activity.