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

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Multiple Choice

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

Fructose-2,6-bisphosphate acts as a powerful allosteric activator of PFK-1, making it a key lever that pushes glycolysis forward when energy is abundant. The level of F2,6BP is controlled by the bifunctional enzyme PFK-2/FBPase-2, which is regulated by hormonal signals. When insulin is high, signaling leads to dephosphorylation and increased kinase activity of PFK-2, raising F2,6BP and strongly activating PFK-1, thereby accelerating glycolysis. In contrast, glucagon triggers phosphorylation of PFK-2, reducing its kinase activity, lowering F2,6BP, and dampening PFK-1 activity to slow glycolysis. This pathway shows how hormones modulate glycolysis by tuning F2,6BP levels and thus PFK-1 activity. Pyruvate kinase is indeed regulated by hormones too, but its control is downstream and often separate from the F2,6BP–PFK-1 axis, so the primary mechanism of hormonal effects on glycolytic flux centers on altering F2,6BP and PFK-1. Therefore, the idea that there is no involvement of F2,6BP in hormonal regulation is not accurate; the hormonal control of glycolysis largely operates through changes in F2,6BP that modulate PFK-1 activity.

Fructose-2,6-bisphosphate acts as a powerful allosteric activator of PFK-1, making it a key lever that pushes glycolysis forward when energy is abundant. The level of F2,6BP is controlled by the bifunctional enzyme PFK-2/FBPase-2, which is regulated by hormonal signals. When insulin is high, signaling leads to dephosphorylation and increased kinase activity of PFK-2, raising F2,6BP and strongly activating PFK-1, thereby accelerating glycolysis. In contrast, glucagon triggers phosphorylation of PFK-2, reducing its kinase activity, lowering F2,6BP, and dampening PFK-1 activity to slow glycolysis. This pathway shows how hormones modulate glycolysis by tuning F2,6BP levels and thus PFK-1 activity. Pyruvate kinase is indeed regulated by hormones too, but its control is downstream and often separate from the F2,6BP–PFK-1 axis, so the primary mechanism of hormonal effects on glycolytic flux centers on altering F2,6BP and PFK-1. Therefore, the idea that there is no involvement of F2,6BP in hormonal regulation is not accurate; the hormonal control of glycolysis largely operates through changes in F2,6BP that modulate PFK-1 activity.

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