A 52-year-old man with chronic alcoholism is brought to the emergency department with confusion, nystagmus, and bilateral lateral rectus palsy. Intravenous glucose was given before thiamine. The deficient vitamin functions as a cofactor for which pair of enzymes?

• A Cystathionine beta-synthase and methionine synthase
• B Pyruvate carboxylase and acetyl-CoA carboxylase
• C Glutamate dehydrogenase and branched-chain alpha-ketoacid dehydrogenase
• D Pyruvate dehydrogenase complex and alpha-ketoglutarate dehydrogenase ✓

Explanation

Thiamine pyrophosphate is the cofactor for oxidative decarboxylation reactions: the pyruvate dehydrogenase complex, alpha-ketoglutarate dehydrogenase, and transketolase of the hexose monophosphate shunt. Pyruvate carboxylase requires biotin, not thiamine, which eliminates option B. The clinical picture is Wernicke encephalopathy, and giving glucose before thiamine can precipitate or worsen it by driving PDH flux with inadequate cofactor.

Reference: Harper's Illustrated Biochemistry, 31st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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