zymogen

n. substance which converts into an enzyme under certain conditions (Biology)

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.
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Zy·mo·gen n. See proenzyme. zymogen an inactive precursor that is converted into an active enzyme by action of an acid or another enzyme or by other [more]Zymogen - Community and Resources

Noun
1. any of a group of compounds that are inactive precursors of enzymes and require some change (such as the hydrolysis of a fragment that masks an active enzyme) to become active
(synonym) proenzyme
(hypernym) organic compound

n. zymogen, substance which converts into an enzyme under certain conditions (Biology)