Cofactors are a non-protein chemical compound that are bound (either tightly or loosely) to a protein and are required for the protein's biological activity.
Cofactors are also often further classified depending on how tightly they bind to the protein:
- loosely-bound cofactors termed coenzymes
- tightly-bound cofactors termed prosthetic groups
Coenzymes are molecules shared by different metabolic pathways and modulate their interactions (eg.: ATP, AMP, NAD/NADH).