Illustrated Glossary of Organic Chemistry

Cofactor: A substance other than a protein that is required for a protein's biological activity. A cofactor which is an organic molecule is further categorized as a coenzyme.

CH3CH2OH
 +


+
Ethanol
   
NAD+
A coenzyme
Acetaldehyde
   
NADH
Oxidation of ethanol to acetaldehyde by alcohol dehydrogenase (an enzyme) uses NAD+ as an oxidizing agent and coenzyme. NAD+ is categorized as a coenzyme because it is an organic molecule (more complex than an inorganic ion).


Carboxypeptidase A, an enzyme that catalyzes hydrolysis of a protein's C-terminal amino acid residue (shown in red), uses Zn2+ as a cofactor. Zn2+ is an inorganic ion and not an organic molecule, and thus not categorized as a coenzyme.