During fasting, hepatic HMG-CoA reductase is rapidly inactivated to conserve ATP and reduce cholesterol synthesis. Which post-translational modification is primarily responsible for this acute regulation?
- A Phosphorylation ✓
- B Ubiquitination
- C Acetylation
- D Glycosylation
Correct answer: A. Phosphorylation
Explanation
HMG-CoA reductase is regulated acutely by phosphorylation via AMP-activated protein kinase (AMPK). Glucagon signaling during fasting activates AMPK, which phosphorylates and inactivates the enzyme to conserve ATP. Sterols and fasting decrease its synthesis and increase degradation, but phosphorylation provides the immediate on-off switch. Ubiquitination leads to proteasomal degradation, which is a slower process.
Reference: Lehninger Principles of Biochemistry, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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