Unit 6

• 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.

Matching the items of List I with List II for Vitamins and other biochemical constituents with special reference to disease diagnosis in domestic animals:

The correct combination is Option 1: (A) - (Il), (B)- (), (C) - (lt), (D) - (IV).

Correct option: (1) (A) - (Il), (B)- (), (C) - (lt), (D) - (IV)