A coenzyme is an organic nonprotein molecule such as derivative of a water soluble vitamin. A coenzyme binds or attaches with a protein molecule (referred to as an apoenzyme). The coenzyme and the apoenzyme together are referred to as a holoenzyme or "an active enzyme".

Coenzymes are often referred to as cofactors. Although the terms can be used synonymously, be aware that the term "cofactor" is also used in haematology as a reference to "factors" in the blood (eg. coagulation factors) and other biochemical systems.

In summary, both coenzymes and cofactors assist enzymes by increasing their rates of reaction (lowering their required energy of activation).

Examples of cofactors. Click on the coenzyme to learn more.
Coenzyme A	Coenzyme Q	Coenzyme B12
NAD+	NADP+	FAD
FMN	FMNH2	FADH2

Coenzyme A (Abbr. CoA)-Coenzyme A is one type of coenzyme that is responsible for metabolism (eg., oxidation) of fatty acids (fats) and thus, energy metabolism. Pantothenic acid functions as a component of Coenzyme A. See also panthothenic acid

 

There is no RDA for CoA. However, the B complex vitamin pantothenic acid, which functions as a component of CoA, and has an RDA of 4-7 mg/day.

Coenzyme Q (Abbr. CoQ)-Coenzyme Q is a derivative of quinone. CoQ is also called ubiquinone becuase is a quinone derivative that is "ubiquitous" or found throughout the biological systems. CoQ functions in accepting hydrogen atoms from FMNH₂ and NADH₂. CoQ also transfers electrons to cytochromes, in the electron transport chain. The electron transport chain is an energy producing cycle that occurs in the mitochondria of cells. Mitochondria are the energy producing organelles or "factories" in each cell.

 

There is no RDA for CoA.

NAD-NAD is the abbreviation for Nicotinamide adenine denucleotide. We discussed niacin in the vitamin section. Niacin is a vitamin required as a component of the coenzymes NAD⁺ and NADP⁺ . These coenzymes¹ function in oxidation-reduction reactions. Oxidation- reduction reactions are simply reactions which involve the transfer of electrons. Reduction is the gain of an electron by an atom or a substance and oxidation is the loss of an electon. Electrons are part of each atom and have a "negative charge". Therefore, if an atom has lost one of its electrons, it has a "net" positive charge. We saw another example of this with chloride portion of sodium chloride. We can see that NAD⁺ and NADP⁺ have a net positive charge, indicated by the "plus sign" (⁺).

¹ NAD is cofactor form (of niacin), acting as a coenzyme.

FMN-FMN is the abbreviation for flavin mononucleotide. FMN is riboflavin 5'-phosphate, and acts as a coenzyme in a number of enzymes. see riboflavin.