1. Cofactor 2. Coenzyme 3. Apoenzyme 4. Holoenzyme

1. Cofactor: A non-protein chemical compound or metallic ion that is required for the activity of certain enzymes.
2. Coenzyme: A type of cofactor that is an organic molecule, often derived from vitamins, that is required for the activity of certain enzymes.
3. Apoenzyme: The protein component of an enzyme that requires a cofactor or coenzyme to become active.
4. Holoenzyme: The active form of an enzyme that consists of both the protein component (apoenzyme) and the necessary cofactor or coenzyme.

Cofactor: A non-protein molecule that is required for enzyme activity.

Coenzyme: A cofactor that is organic and loosely bound to the enzyme.

Apoenzyme: The protein part of an enzyme without its cofactor.

Holoenzyme: The complete enzyme, consisting of the apoenzyme and its cofactor(s).