The inactive precursor of an enzyme that, on reaction with an appropriate kinase or other chemical agent, liberates the enzyme into an active form: As a plasminogen-bound zymogen, CPB2 is synthezised by the liver and is distributed throughout the plasma, or the colourless watery fluid of the blood and lymph.

A secretory particle of a pre-enzyme substance: A zymogen granule can be identified in the cells of synthetic organs, such as salivary glands or the pancreas.