Question

Indicate whether each of the following would be increased or decreased in liver in response to an increase in [cAMP]. Briefly explain why each increase or decrease makes metabolic sense. A. activity of PFK-1 B. activity of FBPase-1 C. activity of glycogen synthase D. activity of phosphorylase kinase E. concentration of β-D-fructose-2,6-bisphosphate  

Answer 1

A. activity of PFK-1: PFK-1, catalyzes the formation of fructose1, 6 biphosphate from the fructose 6 phosphate, which is the irreversible step of glycolysis. PFK-1 is allosterically activated by the cAMP. Thus increased cAMP level ensures efficient glycolysis process to produce more ATP in the cell.

B. activity of FBPase-1: Increased cAMP level causes activation of FBPase-2 and deactivation of PFK-2, which inhibits fructose-2,6-bisphosphate formation from the fructose-6-phosphate (F6P). F6P allosterically inhibit FBpase1, thus gluconeogenesis process is prevented.

C. activity of glycogen synthase: Increased cAMP level inactivates glycogen synthase, thus prevents glycogen synthesis in liver.

D. activity of phosphorylase kinase: Due to the increased cAMP level, phosphorylase kinase is activated, which in turn phosphorylates and activates glycogen phosphorylase results increased glycogen breakdown.

E. concentration of β-D-fructose-2,6-bisphosphate: Increased cAMP level causes activation of FBPase-2 and deactivation of PFK-2, which inhibits fructose-2,6-bisphosphate formation.