Question

Describe the role of the bifunctional enzyme in the reciprocal regulation of glycolysis and gluconeogenesis.

Answer 1

When an enzyme perform both on and off function of a pathway it is called as bifunctional enzyme. Phosphofructokinase -2 (PFK-2)/ fructose2,6- bisphosphatase (FBPase-2) is a best example for that. This is a potent regulator of glycolysis. This indirectly regulate this pathway.

Fructose 2,6-bisphosphate (F2,6 -BP) regulates the glycolysis directly. This molecule gets activated or deactivated by phosphorylation or dephosphorylation respectively.

# When F2,6-BP is active, it stimulates glycolysis and inhibits gluconeogenesis. Here PFK-2 adds one phosphate to F6-P and convert into F2,6-BP (Active).

# When F2,6-BP is inactive, it inhibits glycolysis and stimulates gluconeogenesis. Here FBPase-2 removes a phosphate from F2,6-BP and convert it into F6-P (Inactive). This cannot induce glycolysis.

So the phosporylation and dephosphorylation of F6-P/ F2,6-BP switches the reciprocal regulation glycolysis and gluconeogenesis.