Coenzyme is an organic non-protein molecule that associates with an enzyme molecule in catalysing 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 protein part of 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 catalyses the same reaction but differ from each other in such properties as substrate affinity and maximun rates of enzyme-substrate reaction.