During prolonged starvation, the liver switches from glucose oxidation to fatty acid oxidation. The key regulatory molecule that signals high beta-oxidation flux and inhibits malonyl-CoA synthesis (thereby preventing futile cycling) is:

• A Acetyl-CoA (via allosteric inhibition of ACC)
• B Citrate allosterically activating acetyl-CoA carboxylase
• C AMP-activated protein kinase (AMPK) phosphorylating and inactivating ACC ✓
• D Malonyl-CoA directly inhibiting CPT-I

Explanation

AMPK (AMP-activated protein kinase) is the cellular energy sensor — activated when AMP/ADP rises during energy deficit (starvation). AMPK phosphorylates acetyl-CoA carboxylase (ACC), inactivating it, which reduces malonyl-CoA production. Since malonyl-CoA inhibits carnitine palmitoyl transferase I (CPT-I), its reduction relieves CPT-I and allows fatty acids to enter mitochondria for beta-oxidation. Citrate activates (not inhibits) ACC in the fed state, promoting fatty acid synthesis. Malonyl-CoA inhibiting CPT-I is the mechanism of prevention of simultaneous FA synthesis and oxidation, but the question asks what prevents malonyl-CoA synthesis.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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