Biochemistry, molecular genetics, and biology glossary terms for Companion Sites.


A zymogen or proenzyme, is an inactive enzyme precursor that requires a configurational or biochemical change for activation. Typically, cleavage of a portion of the precursor enzyme takes place within a lysosome, releasing the activation peptide.

Examples of zymogens are trypsinogen, chymotrypsinogen, pepsinogen, proalbumin, most proteins of the coagulation system, some proteins of the complement system, the caspases.

. . . since 10/06/06