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. So, the correct answer is 'Coenzyme'.

Holoenzymes are the active forms of enzymes. Enzymes that require a cofactor but are not bound by one are called apoenzymes. Holoenzymes represent the apoenzyme bound to its necessary cofactors or prosthetic groups.
Apoenzyme or apoprotein is an enzymatically inactive protein part of an enzyme, which requires a cofactor for its activity. Apart from catalytic RNA, most of the enzymes are proteins. Not all the enzymes require a cofactor. Enzymes that do not require any cofactor are known as simple enzymes, e.g. pepsin, trypsin, etc.
Isozymes (also known as isoenzymes) are homologous enzymes that catalyze the same reaction but differ in structure. ... For example, the isoenzymes of lactate dehydrogenase in animal organs are different in term of their amino acid sequences and the level of their expression.
A coenzyme is an organic non-protein compound that binds with an enzyme to catalyze a reaction. Coenzymes are often broadly called cofactors, but they are chemically different. A coenzyme cannot function alone, but can be reused several times when paired with an enzyme.
An enzyme without a coenzyme is called an apoenzyme. Without coenzymes or cofactors, enzymes cannot catalyze reactions effectively. In fact, the enzyme may not function at all. If reactions cannot occur at the normal catalyzed rate, then an organism will have difficulty sustaining life.

When an enzyme gains a coenzyme, it then becomes a holoenzyme, or active enzyme. Active enzymes change substrates into the products an organism needs to carry out essential functions, whether chemical or physiological. Coenzymes, like enzymes, can be reused and recycled without changing reaction rate or effectiveness. They attach to a portion of the active site on an enzyme, which enables the catalyzed reaction to occur. When an enzyme is denatured by extreme temperature or pH, the coenzyme can no longer attach to the active site.