Compare allosteric regulation by fructose-2,6-bisphosphate on PFK-1 with hormonal control of glycolysis by insulin and glucagon.

• A. Fructose-2,6-bisphosphate strongly activates PFK-1, increasing glycolysis; insulin promotes dephosphorylation of PFK-2, raising F2,6BP and glycolysis; glucagon promotes phosphorylation of PFK-2 lowering F2,6BP and reducing glycolysis.
• B. F2,6BP inhibits PFK-1, reducing glycolysis; insulin and glucagon have no effect on glycolysis.
• C. F2,6BP has no effect on glycolysis; insulin/glucagon regulate only hexokinase.
• D. Insulin and glucagon directly act on pyruvate kinase with no F2,6BP involvement.

Answer: (D)