(a) Many enzymes show catalytic activity only in association with certain non-protein substances. Such substances are called cofactors. Example : Simple metal ions, e.g., `Mg^(++)`.
(b) Apoenzymes. The enzymes which work only in the presence of cofactors are called apoenzymes.
Coenzyme. An organic non-protein cofactor which is easily separable from the apoenzyme is called coenzyme.
Prosthetic group. The non-protein organic cofactor that is tightly bound to and non-dissociable from the enzyme is called prosthetic group.
