Ketone body synthesis occurs almost exclusively in the liver. Which enzymatic property of hepatocytes explains this tissue specificity?

• A Hepatocytes uniquely express acetyl-CoA carboxylase
• B Hepatocytes are the only cells expressing HMG-CoA reductase
• C Only liver possesses carnitine palmitoyltransferase-1
• D Hepatic mitochondria contain HMG-CoA synthase isoform 2, absent from extrahepatic tissues ✓

Explanation

Ketogenesis requires mitochondrial HMG-CoA synthase (the mitochondrial isoform, HMGCS2), which is expressed almost exclusively in hepatocytes. Extrahepatic tissues have the cytosolic isoform for cholesterol synthesis but lack the mitochondrial enzyme needed to form HMG-CoA destined for HMG-CoA lyase. HMG-CoA reductase is cytosolic and involved in sterol synthesis, not ketogenesis, so option B describes a different pathway. CPT-1 and ACC are widely distributed.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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