Which term describes an enzyme that is bound to cofactors and is active?

• A. Apoenzyme
• B. Holoenzyme
• C. Prosthetic group
• D. Cofactor

Answer: (B)

The active form of an enzyme requires a non-protein helper. When the protein alone is present, it’s called an apoenzyme and is inactive without its partner molecules. Once the cofactor binds, the complex becomes the holoenzyme, the active form. Cofactors can be inorganic ions or organic molecules, and they can be tightly or loosely bound. A prosthetic group is a cofactor that remains tightly bound to the enzyme, essentially part of the enzyme’s structure, which is a way cofactors contribute to forming a functional holoenzyme. So, in this context, the enzyme bound to its cofactors and capable of catalysis is the holoenzyme.