Question

Which of these vitamin derivatives is involved in oxidative decarboxylation reaction?

• A. Thiamine
• B. Folic acid
• C. Riboflavin
• D. Tocopherol

Hint:

Whenever you see "oxidative decarboxylation of \(\alpha\)-keto acids", think of Thiamine Pyrophosphate (TPP), the coenzyme derivative of Vitamin \(\text{B}_1\).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Oxidative decarboxylation reactions require specific coenzymes to stabilize the transient negative charge on intermediate carbon compounds during the cleavage of carbon-carbon bonds.

Step 2: Detailed Explanation:
1. Thiamine (Vitamin \(\text{B}_1\)) is converted into its active coenzyme form, Thiamine Pyrophosphate (TPP), inside cells.
2. TPP contains a thiazolium ring with an acidic carbon. This carbon easily deprotonates to form a carbanion, which acts as a nucleophile to attack the carbonyl carbon of \(\alpha\)-keto acids (such as pyruvate and \(\alpha\)-ketoglutarate).
3. This specific mechanism is essential for the oxidative decarboxylation reactions catalyzed by:
- Pyruvate Dehydrogenase complex (converting pyruvate to acetyl-CoA)
- \(\alpha\)-Ketoglutarate Dehydrogenase complex (in the TCA cycle)
Folic acid is involved in one-carbon transfer, Riboflavin (as FAD/FMN) in redox reactions, and Tocopherol acts as an antioxidant.

Step 3: Final Answer:
The correct option is 1, which corresponds to Thiamine.