CO-ENZYMES

 

INTRODUCTION: Enzymes may be simple proteins, or complex enzymes, containing a non-protein part, called the prosthetic group. The prosthetic group is called the co-enzyme and therefore may be non-proteins in nature. Usually the prosthetic group is heat stable than the protein component of the enzyme. The protein part of the enzyme is then named the apo-enzyme which is heat labile and then the two portions combined together is called the holo-enzyme.

CLASSIFICATION OF CO-ENZYMES: Co-enzymes may be divided into two groups;

1) Those taking part in reactions catalyzed by oxidoreductases by donating or accepting hydrogen atoms or electrons.

2) Those co-enzymes taking part in reactions transferring groups other than hydrogen.

In the first group, the change occurring in the substrate is counter-balanced by the co-enzymes. Therefore, such co-enzymes may be considered as co-substrates or secondary substrates.

NICOTINAMIDE ADENINE DINUCLEOTIDE (NAD+): This is a co-enzyme synthesized from Nicotinamide, a member of vitamin B complex. The reversible reaction of lactate to pyruvate is catalyzed by the enzyme lactate dehydrogenase, but the actual transfer of hydrogen is taking place on the co-enzyme, NAD⁺.

In this case, two hydrogen atoms are removed from lactate, out of which one hydrogen and two electrons are accepted by the NAD⁺ to form NADH, and the remaining H⁺ is released into the surrounding medium.

SECOND GROUP OF CO-ENZYMES: These co-enzymes take part in reactions transferring groups other than hydrogen. A particular group or radical is transferred from the substrate to another substrate. Most of them belong to vitamin B complex group.

ADENOSINE TRIPHOSPHATE (ATP): ATP is considered to be the energy currency in the body. In the ATP molecule, the second and third phosphate bonds are ‘high energy' bonds. During the oxidation of food stuffs, energy is released, a part of which is stored as chemical energy in the form of ATP. The endergonic reactions are carried out with the help of energy released from hydrolysis of ATP.

METALLO-ENZYMES: These are enzymes which require certain metal ions for their activity. In certain cases, such as copper in Tyrosinase, the metal is tightly bound with the enzyme. In other cases, even without the metal ion, enzyme may be active; but when the metal ion is added, the activity is enhanced. They are called ion-activated enzymes, for example, calcium ions will activate pancreatic lipase.

Co-factors: The term co-factor is used as a collective term to include co-enzymes and metal ions. Co-enzyme is an organic co-factor.

RELATED;

1. LACTATE

2. PYRUVATE

3. BIOCHEMISTRY OF ENZYMES

4. BIOMOLECULES AND CHEMICALS OF LIFE

REFERENCES