Fructose-2,6-bisphosphate (F-2,6-BP) is a potent allosteric regulator of glycolysis and gluconeogenesis. In the FED state, insulin promotes F-2,6-BP synthesis by:

• A Activating glucokinase to generate more F-6-P substrate for PFK-2
• B Glucagon activates PKA which phosphorylates PFK-2, increasing F-2,6-BP synthesis
• C Insulin inhibits phosphoprotein phosphatase, keeping PFK-2 phosphorylated and active
• D Activating phosphofructokinase-2 (PFK-2) by dephosphorylation via PP2A, increasing F-2,6-BP which activates PFK-1 and inhibits FBPase-1 ✓

Explanation

PFK-2/FBPase-2 is a bifunctional enzyme; when phosphorylated (by PKA, in glucagon state), the FBPase-2 activity dominates, lowering F-2,6-BP. In the fed/insulin state, PP2A dephosphorylates PFK-2/FBPase-2, activating PFK-2 kinase activity, generating F-2,6-BP. High F-2,6-BP allosterically activates PFK-1 (key glycolytic enzyme) and inhibits FBPase-1 (gluconeogenic enzyme), coordinately promoting glycolysis and suppressing gluconeogenesis.

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

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