/zuy"meuh jeuhn, -jen'/, n. Biochem.
any of various enzyme precursor molecules that may change into an enzyme as a result of catalytic change. Also called proenzyme.
[ < G (1875); see ZYMO-, -GEN]

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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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also called  Proenzyme,  

      any of a group of proteins that display no catalytic activity but are transformed within an organism into enzymes, especially those that catalyze reactions involving the breakdown of proteins. Trypsinogen and chymotrypsinogen, zymogens secreted by the pancreas, are activated in the intestinal tract to trypsin and chymotrypsin. Activation is effected by the cleavage of one or more peptide bonds of the zymogen molecule and may be catalyzed by a separate enzyme—e.g., enterokinase converts trypsinogen to trypsin—or by the active form itself—trypsin also converts trypsinogen to more trypsin. Zymogenic cells synthesize and store zymogens in inactive form.

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Universalium. 2010.

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