Despite active ketogenesis during prolonged fasting, the liver exports essentially all ketone bodies because it cannot consume them itself. The reason is hepatic absence of:

• A Beta-hydroxybutyrate dehydrogenase
• B 3-hydroxy-3-methylglutaryl-CoA lyase
• C Acetoacetyl-CoA thiolase
• D Succinyl-CoA:acetoacetate CoA transferase (thiophorase) ✓

Explanation

Extrahepatic tissues activate acetoacetate by transferring CoA from succinyl-CoA, a reaction catalysed by thiophorase (SCOT). The liver expresses negligible thiophorase, so it cannot reconvert acetoacetate to acetoacetyl-CoA, ensuring net ketone export to brain and muscle. Beta-hydroxybutyrate dehydrogenase and acetoacetyl-CoA thiolase are present in liver and function in ketone production, while HMG-CoA lyase acts upstream in synthesis.

Reference: Lehninger Principles of Biochemistry, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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