What is the definition of apoenzyme?

Apoenzyme:

An apoenzyme is a protein molecule that lacks its cofactor or coenzyme, and therefore cannot catalyze a chemical reaction. Coenzymes and cofactors are non-protein molecules that are required for the proper functioning of enzymes. They can be metal ions, organic molecules, or other inorganic compounds.

When an apoenzyme binds to its cofactor or coenzyme, it becomes an active enzyme, and can catalyze a specific chemical reaction. The cofactor or coenzyme may participate directly in the reaction, or it may help to stabilize the enzyme structure and create the proper environment for the reaction to occur.

Some enzymes require only a single cofactor or coenzyme, while others may require multiple cofactors or coenzymes to function properly. Cofactors and coenzymes are typically recycled during the course of an enzyme reaction, so they do not need to be consumed in stoichiometric amounts.