) 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: