In a person starved for 10 days, the circulating ratio of beta-hydroxybutyrate to acetoacetate rises markedly compared with the fed state. The biochemical basis of this rise is:

• A Induction of HMG-CoA reductase in hepatocytes
• B Selective renal clearance of acetoacetate
• C High mitochondrial NADH generated by beta-oxidation drives reduction of acetoacetate ✓
• D Activation of succinyl-CoA transferase in the liver

Explanation

During starvation, unrestrained beta-oxidation floods hepatic mitochondria with NADH. The enzyme beta-hydroxybutyrate dehydrogenase catalyses a reversible reaction whose equilibrium depends on the NADH:NAD+ ratio, so abundant NADH shifts acetoacetate toward beta-hydroxybutyrate. The ratio can reach 3:1 or higher. The liver itself cannot use ketones because it lacks thiophorase (succinyl-CoA transferase), which makes option D tempting but irrelevant to the ratio change.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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