zymogen

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.