Most of the vitamins function as

Options

A. Holoenzyme
B. Enzymes
C. Hormones
D. Coenzymes

Explanation

**Step-by-Step Solution:**

1. **Understanding Vitamins**: Vitamins are organic compounds that are essential for normal growth and nutrition. They are required in small quantities in the diet because they cannot be synthesized by the body.

2. **Functions of Vitamins**: Most vitamins play crucial roles in various biochemical processes. They can function as:
- **Co-enzymes**: These are non-protein molecules that assist enzymes in catalyzing reactions. They bind to the enzyme and help in the transformation of substrates into products.
- **Holo-enzymes**: This term refers to the complete enzyme that includes the apo-enzyme (the protein part) and the co-factor (the non-protein part, which can be a co-enzyme).
- **Hormones**: Some vitamins can act as hormones, which are signaling molecules that regulate physiological processes in the body.

3. **Examples of Vitamins as Co-enzymes**:
- Thiamine (Vitamin B1) acts as a co-enzyme in the enzyme pyruvate dehydrogenase, which is crucial in the metabolic pathway of converting pyruvate into acetyl-CoA.
- Riboflavin (Vitamin B2) is another example that functions as a co-enzyme in various reactions.

4. **Conclusion**: Based on the functions of vitamins, it can be concluded that most of them primarily function as co-enzymes, facilitating enzymatic reactions in the body.

**Final Answer**: Most of the vitamins function as co-enzymes.

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