Any intermediate or product resulting from metabolism. The term 'metabolite' subsumes the classes commonly known as primary and secondary metabolites.
A tightly bound, specific nonpolypeptide unit in a protein determining and involved in its biological activity.
An organic molecule or ion (usually a metal ion) that is required by an enzyme for its activity. It may be attached either loosely (coenzyme) or tightly (prosthetic group).
(via porphyrins )