During prolonged starvation, hepatic ketone body production rises sharply. Which enzyme catalyzes the rate-limiting step of hepatic ketogenesis?
- A HMG-CoA reductase
- B Cytoplasmic HMG-CoA synthase
- C Mitochondrial HMG-CoA synthase ✓
- D HMG-CoA lyase
Correct answer: C. Mitochondrial HMG-CoA synthase
Explanation
Mitochondrial HMG-CoA synthase converts acetyl-CoA and acetoacetyl-CoA to HMG-CoA and is the committed, rate-limiting enzyme of ketogenesis; it is induced by glucagon and free fatty acids during fasting. The cytoplasmic isoform (option B) serves cholesterol synthesis instead. HMG-CoA reductase belongs to cholesterol biosynthesis, and HMG-CoA lyase acts later, cleaving HMG-CoA to acetoacetate.
Reference: Lehninger Principles of Biochemistry, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.