constitutive enzyme An enzyme that is always produced whether or not a suitable substrate is present (enzymes functioning by forming a complex with the substrate, see LOCK-AND-KEY THEORY). Such enzymes are sometimes produced by particular regulatory mutants which, though not affecting the structure of the enzyme, instead affect the process by which its synthesis occurs. An example is the lac-operon, which controls the synthesis of three enzymes: (betagalactosidase, permease, and acetylase) enzymes that are involved in the lactose metabolism of the bacterium Escherichia coli.

constitutive enzyme An enzyme that is always produced whether or not a suitable substrate is present. Such enzymes are sometimes produced by particular regulatory mutants which, though not affecting the structure of the enzyme, instead affect the process by which its synthesis occurs. An example is the lac-operon, which controls the synthesis of three enzymes (beta-galactosidase, permease, and acetylase): enzymes that are involved in the lactose metabolism of the bacterium Escherichia coli.