Question

Which is the pair of the enzyme activities most significantly affected by glucagon- and insulin-dependent phosphorylation and dephosphorylation of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFKFB)?

a. hexokinas ::::: glucose-6-phosphatase
b. phosphofructokinase ::::: Fructose-1,6-bisphosphatase
c. pyruvate kinase :::::: pyruvate carboxylase
d. glycogen synthase ::::: glycogen phosphorylase
e. None of these

Answer 1

b. Phosphofructokinase; Fructose-1,6-bisphosphatase

Step-by-step explanation:

Glucagon is a hormone which functions to initiate gluconeogenesis whwreas insulin functions to initiate glycolysis.

Fructose-2,6-bisphosphate (F26BP) is an allosteric regulator of the glycolytic and gluconeogenic enzymes phosphofructokinase-1 (PFK-1) and fructose-1,6-bisphosphatase (FBPase-1).

It stimulates glycolysis and inhibits gluconeogenesis by binding to its allosteric site on phosphofructokinase-1 reducing its affinity for the allosteric inhibitors ATP and citrate .

It is formed by phosphorylation of fructose-6-phosphate catalyzed by phosphofructokinase-2 and is broken down by fructose-2,6-bisphosphatase which are two separate enzymatic activities of a single, bifunctional protein (PFK-2/FBPase-2).

Phosphorylation of PFK-2/FBPase-2 due to glucagon release enhances its FBPase-2 activity thereby stimulating gluconeogenesis and inhibiting glycolysis.

Dephosphsorylation of PFK-2/FBPase-2 due to insulin release enhances its PFK-2 activity, thereby stimulating glycolysis and inhibiting gluconeogenesis.