Maple syrup urine disease (MSUD) results from deficiency of branched-chain α-keto acid dehydrogenase (BCKAD). This enzyme complex is analogous to pyruvate dehydrogenase and requires the same five cofactors. Which of the following cofactors is NOT required by BCKAD?

• A Biotin ✓
• B Thiamine pyrophosphate (TPP)
• C Lipoic acid
• D FAD

Explanation

BCKAD and pyruvate dehydrogenase share the same cofactors: TPP (E1 component), lipoic acid (E2), FAD (E3 — dihydrolipoyl dehydrogenase), NAD+, and CoA. Biotin is NOT a cofactor for either; biotin is required by biotin-dependent carboxylases such as pyruvate carboxylase, acetyl-CoA carboxylase, and propionyl-CoA carboxylase. A subset of MSUD patients respond to thiamine supplementation because high-dose thiamine stabilises the E1 (decarboxylase) component — this is the basis for 'thiamine-responsive MSUD'.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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