During prolonged fasting, hepatic gluconeogenesis is maximally active. Which allosteric effector directly inhibits pyruvate kinase (L isoform) to prevent futile cycling between PEP and pyruvate?
- A AMP
- B Fructose-1,6-bisphosphate
- C Alanine ✓
- D Acetyl-CoA
Correct answer: C. Alanine
Explanation
Alanine allosterically inhibits the hepatic L isoform of pyruvate kinase, preventing re-conversion of PEP to pyruvate. This ensures that PEP generated gluconeogenically continues toward glucose synthesis rather than being lost to glycolysis. Fructose-1,6-bisphosphate is a feed-forward activator of pyruvate kinase; AMP activates PFK-1. Acetyl-CoA activates pyruvate carboxylase, not pyruvate kinase.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.