Anaplerotic reactions replenish TCA cycle intermediates withdrawn for biosynthesis. Which enzyme carries out the single most important anaplerotic reaction in mammals, and how is it regulated?
- A Pyruvate carboxylase, activated by acetyl-CoA ✓
- B Glutamate dehydrogenase, activated by ATP
- C Malic enzyme, activated by NADH
- D Propionyl-CoA carboxylase, activated by insulin
Correct answer: A. Pyruvate carboxylase, activated by acetyl-CoA
Explanation
Pyruvate carboxylase converts pyruvate to oxaloacetate using ATP and biotin, and it is the major anaplerotic enzyme. It is allosterically activated by acetyl-CoA, an elegant feedback signal: accumulating acetyl-CoA signals that oxaloacetate is limiting for citrate synthase. Glutamate dehydrogenase and propionyl-CoA carboxylase contribute intermediates but are not the primary regulated anaplerotic route.
Reference: Lehninger Principles of Biochemistry, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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