An organic substance bound to an enzyme and essential for its activity is called:
(a) coenzyme (b) holoenzyme
(c) apoenzyme (d) isoenzyme
(a) Coenzyme is an organic nonprotein molecule that associates with an enzyme molecule in catalsying biochemical reactions. It usually participates in the substrate-enzyme interaction by donating or accepting certain chemical groups. Holoenzyme is a complex comprising of enzyme molecule and its cofactor. The enzyme is catalytically active in this state. Apoenzyme is an inactive enzyme that must associate with a specific cofactor molecule in order to function. Isoenzyme or isozyme is one of the several forms of an enzyme that catalyse the same reaction but differ from each other in such properties as substrate affinity and maximum rates of enzyme-substrate reaction.