11
Vitamin B12-dependent enzymes are
(A) . Methyl malonyl CoA mutase
(B) . Pyruvate dehydrogenase
(C) . Methionine synthase
(D) . Catalase
Choose the correct answer from the options given below:
EXPLANATION
DNA Damage, Mutations & Repair Systems
- Vitamin $\text{B}_{12}$ (Cobalamin) Dependent Enzymes: In mammalian cells, only two enzymes require cobalamin coenzymes:
- Methylmalonyl-CoA mutase: Requires adenosylcobalamin (5'-deoxyadenosylcobalamin) to convert L-methylmalonyl-CoA to succinyl-CoA in propionate and odd-chain fatty acid metabolism.
- Methionine synthase (homocysteine methyltransferase): Requires methylcobalamin to transfer a methyl group from $N^5$-methyltetrahydrofolate to homocysteine, forming methionine and regenerating tetrahydrofolate (THF).
- Other Enzymes:
- Pyruvate dehydrogenase: Requires TPP (Vitamin $\text{B}_1$), Lipoic acid, FAD (Vitamin $\text{B}_2$), $\text{NAD}^+$ (Vitamin $\text{B}_3$), and CoA (Vitamin $\text{B}_5$).
- Catalase: Heme metalloenzyme (iron-dependent).
- Conclusion: Therefore, (A) and (C) only are vitamin $\text{B}_{12}$-dependent enzymes.
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