The difference between an apoenzyme and a holoenzyme is based on whether the enzyme has its helper molecule (cofactor or coenzyme) attached or not.
Apoenzyme:
- It is the inactive form of an enzyme.
- It is made only of the protein part, without any cofactor or coenzyme.
- It cannot catalyze reactions until the helper molecule binds to it.
Holoenzyme:
- It is the active form of the enzyme.
- It consists of the apoenzyme plus its cofactor or coenzyme.
- It can catalyze the reaction because the complete structure is functional.
In simple terms:
- Apoenzyme = enzyme without its helper → inactive
- Holoenzyme = enzyme with its helper → active
Example:
When the enzyme carbonic anhydrase binds with its zinc ion (cofactor), it becomes active — this complete form is the holoenzyme.