Answer:
3. apoenzyme
Step-by-step explanation:
Apoenzymes -
It is the inactive form of the enzyme , and it binds with the substrate which have affinity like of the holoenzyme , but is does not have the capability to convert the substrate to product .
The binding process may lead to some conformational changes in the apoenzyme , which the method of fluorescence can detect .
hence , the protein portion of the enzyme is the 3. apoenzyme .