Glucagon, PFK-2, and fructose-2,6-bisphosphate
During fasting, glucagon raises cAMP in hepatocytes, and the bifunctional enzyme PFK-2/FBPase-2 is phosphorylated. What is the net effect on glucose metabolism?
Answer B: explanation for every choice
A
Rising fructose-2,6-bisphosphate is the fed-state response to insulin.
B
Correct. Phosphorylation turns on the phosphatase activity, lowering fructose-2,6-bisphosphate. That removes activation of PFK-1 and relieves inhibition of fructose-1,6-bisphosphatase.
C
Lower fructose-2,6-bisphosphate releases fructose-1,6-bisphosphatase, so gluconeogenesis increases.
D
PFK-1 is regulated allosterically, not by PKA phosphorylation.
TakeawayFasted liver: low F2,6BP → gluconeogenesis on, glycolysis off.
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Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID bb156.