What is a holoenzyme?

A holoenzyme is an active enzyme made up of both a protein component, called an apoenzyme, and a non-protein component, called a cofactor. The term "holo" means whole, indicating that the holoenzyme is the complete and functional version of the enzyme.

Cofactors can include metal ions, organic molecules like vitamins and coenzymes, or a combination of both. Without the cofactor, the apoenzyme alone is inactive. However, when the cofactor binds to the apoenzyme, the resulting holoenzyme undergoes a conformational change that activates its catalytic activity.

The function of a holoenzyme depends on both its protein and non-protein components, and their specific interactions. Many enzymes require a specific cofactor to function properly, and some have multiple cofactors that work together to catalyze reactions.

Holoenzymes can be either constitutive (always present in a cell) or induced (produced in response to specific signals). They play important roles in cellular metabolism, including the breakdown of molecules for energy production and the synthesis of larger molecules.