Coenzymes
Enzymes may be simple proteins, or complex enzymes. A complex enzyme contains a non-protein part, called as prosthetic group (co-enzymes). Coenzymes are heat stable low molecular weight organic compound. The combined form of protein and the co-enzyme are called as holo-enzyme. The heat labile or unstable part of the holo-enzyme is called as apo-enzyme. The apo-enzyme gives necessary three dimensional structures required for the enzymatic chemical reaction. Co-enzymes are very essential for the biological activities of the enzyme. Co-enzymes combine loosely with apo-enzyme and are released easily by dialysis. Most of the co-enzymes are derivatives of vitamin B complex group of substance. One molecule of the co-enzyme with its enzyme is sufficient to convert a large group of substrate. Co-enzymes are further divided into two groups. The first groups of co-enzymes are a part of reaction catalyzed by oxidoreductase by donating or accepting hydrogen atoms or electrons. The first group of co-enzymes are also called as co-substrates or secondary substrates. Because they are involved in counterbalance in change occurring in the substrate. The second group of co-enzymes involves in reactions transferring groups other than hydrogen.
Role of Coenzymes
The functional role of coenzymes is to act as transporters of chemical groups from one reactant to another. The chemical groups carried can be as simple as the hydride ion (H+ + 2e-) carried by NAD or the mole of hydrogen carried by FAD; or they can be even more complex than the amine (-NH2) carried by pyridoxal phosphate. Since coenzymes are chemically changed as a consequence of enzyme action, it is often useful to consider coenzymes to be a special class of substrates, or second substrates, which are common to many different holoenzymes. In all cases, the coenzymes donate the carried chemical grouping to an acceptor molecule and are thus regenerated to their original form. This regeneration of coenzyme and holoenzyme fulfills the definition of an enzyme as a chemical catalyst, since (unlike the usual substrates, which are used up
during the course of a reaction) coenzymes are generally regenerated.
Intext Quections
1. Non protein part of complex enzymes is called as ……………..
2. Combination of …………….. and …………….. are called as holo enzymes.
3. Co-enzymes are heat stable low molecular weight …………….. compound.
4. There are …………….. groups of co-enzymes.
