Introduction
Enzymes are biological catalysts that speed up chemical reactions in the body. Many enzymes require additional molecules known as cofactors to function properly. Two of the most important cofactors are NAD (Nicotinamide Adenine Dinucleotide) and FAD (Flavin Adenine Dinucleotide). These are involved in oxidation-reduction (redox) reactions and are derived from vitamins. In this answer, we’ll explore two enzyme examples for each cofactor and the vitamins from which they are made.
1. NAD-Dependent Enzymes
NAD functions as an electron carrier in many metabolic pathways like glycolysis, the citric acid cycle, and oxidative phosphorylation.
Examples:
- Lactate Dehydrogenase
- Function: Converts pyruvate to lactate during anaerobic respiration.
- Uses NAD⁺ to accept electrons and form NADH.
- Alcohol Dehydrogenase
- Function: Converts ethanol to acetaldehyde in the liver.
- Uses NAD⁺ as a coenzyme for the oxidation reaction.
Vitamin Source:
- Niacin (Vitamin B3) is the precursor of NAD.
- A deficiency in niacin can lead to pellagra, which causes dermatitis, diarrhea, and dementia.
2. FAD-Dependent Enzymes
FAD is another important redox coenzyme. It can accept two electrons and two protons, and it remains tightly bound to the enzyme.
Examples:
- Succinate Dehydrogenase
- Function: Catalyzes the conversion of succinate to fumarate in the citric acid cycle.
- FAD accepts electrons and is reduced to FADH₂.
- Acyl-CoA Dehydrogenase
- Function: Involved in the beta-oxidation of fatty acids.
- Uses FAD to carry electrons during fatty acid breakdown.
Vitamin Source:
- Riboflavin (Vitamin B2) is the precursor of FAD.
- Riboflavin deficiency can result in symptoms like sore throat, cracks in the lips, and inflammation of the mouth and tongue.
Summary Table
| Cofactor | Enzyme Examples | Vitamin Source |
|---|---|---|
| NAD | Lactate Dehydrogenase, Alcohol Dehydrogenase | Niacin (Vitamin B3) |
| FAD | Succinate Dehydrogenase, Acyl-CoA Dehydrogenase | Riboflavin (Vitamin B2) |
Conclusion
NAD and FAD are essential cofactors involved in numerous metabolic pathways. They act as electron carriers and are vital for cellular respiration and energy production. These cofactors are derived from the B-complex vitamins niacin and riboflavin, respectively. Adequate intake of these vitamins is important to support the enzymes that keep our metabolism running smoothly.