[zahy-muh-juhn, -jen]
or proenzyme

Any of a class of proteins that are secreted by cells and are inactive precursors of enzymes. Transformation into active enzymes occurs as one or more peptide bonds in the zymogen are cleaved. Examples include trypsinogen and chymotrypsinogen, secreted by the pancreas and converted by proteolysis in the small intestine into the active enzymes trypsin and chymotrypsin; and numerous coagulation factors.

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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.


Examples of zymogens:

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