Question: 149. The protein portion of an enzyme is called:
(1) Cofactor
(2) Coenzyme
(3) Apoenzyme
(4) Prosthetic group
Answer: Option (3)
Explanation:
Enzymes may consist of only a protein component or a protein component combined with a non-protein component.
The protein part of an enzyme, which is inactive on its own, is called the apoenzyme.
When the apoenzyme binds with its non-protein part—either a cofactor, coenzyme, or prosthetic group—it becomes an active holoenzyme.
Thus, the protein portion alone is known as the apoenzyme.