Coenzymes

A Coenzyme' (cofactor) is a low molecular weight non-protein structure attached to the protein chain of an enzyme. Coenzymes play an important role in the transfer of hydrogen atoms, electrons, or groups of atoms during an enzyme-catalyzed reaction. According to the method of binding to the protein part of the enzyme, we distinguish:
 * dissociable coenzymes
 * prosthetic groups

Dissociable coenzymes
They are kept in contact with the enzyme by a non-covalent interaction. They can easily separate from the original enzyme molecule and bind to another. These include, for example, NAD+ or NADP+.

Prosthetic groups
They are structures firmly bound to the enzyme mainly covalent bonds. The character of this bond makes the prosthetic group a stable part of the enzyme. Examples include FMN, FAD and lipoic acid.



Action of coenzymes
It is conditioned by two reactions. In the course of these two reactions, on the one hand, reaction catalysis takes place, on the other hand, simultaneous regeneration of the coenzyme. As mentioned above, we distinguish two types of coenzymes.

The two types of coenzymes differ in the way they are regenerated.

Catalysis and regeneration of dissociable coenzymes
First, dissociable coenzyme K, bound to apoenzyme E1, accepts the transferred group X from the substrate S1. Next, the K&minus;X complex binds to the second apoenzyme E2 and transfers the transferred X group in this form to the S2 product. At the same time, coenzyme K is regenerated

Catalysis and regeneration of prosthetic groups
The course of the reaction with prosthetic groups is different due to their strong binding to the apoenzyme. The main difference is that only one apoenzyme participates in the catalysis of both reactions.

Functions of coenzymes
Coenzymes are important for the functions of enzymes that catalyze oxidation-reduction events (oxidoreductases), or enzymes catalyzing the transfer of groups (transferases).

Coenzymes of oxidoreductases
These coenzymes are involved in the transfer of a hydrogen atom or electrons.

Transferase coenzymes
These coenzymes allow the transfer of groups.

Related Articles

 * Enzymes
 * Vitamins
 * Enzyme Cofactors