Epinephrine glycolysis stimulation

In muscle, epinephrine stimulates glycogen breakdown and glycolysis, providing ATP to support contraction. 

Glucagon and epinephrine also regulate pseudocycle II so as to stimulate gluconeogenesis while inhibiting glycolysis. They do this through a chain of reactions that results in a lowering of the concentration of the allosteric effector fructose-2,6-bisphosphate. This effector stimulates phosphofructokinase while it inhibits fructose bisphosphate phosphatase. 

Epinephrine increases muscle glycolysis, and therefore blood lactic acid production and an amplified Cori cycle. In the liver, epinephrine stimulates gluconeogenesis and blood glucose will therefore rise. 

F-2,6-BE Thus, F-2,6-BP levels are decreased and phosphofructokinase activity is decreased. In liver and muscle, F-2,6-BP is the major allosteric activator of phosphofructokinase. In skeletal muscle, however, the kinase responsible for the synthesis of F-2,6-BP is activated, not inhibited, by cyclic AME Thus, muscle sees an increase in glycolysis following epinephrine stimulation, while the liver experiences a decrease in glycolytic activity. In both tissues, glycogen phosphorylase is activated and glycogenolysis occurs. Under these conditions, glucose is utilized in muscle for ATP production relative to contractile activity, while the liver produces glucose for export to the blood. 

Phosphorylation of the PFK2/FBPase-2 enzyme by cAPK requires cAMP. Levels of cAMP in the cell can be modulated hormonally. Glucagon and epinephrine increase cellular cAMP levels (favor gluconeogenesis), whereas insulin, decreases cellular cAMP levels, favoring removal of phosphates (stimulates glycolysis). 

So, when epinephrine or glucagon stimulates cells -> cAMP is produced ->cAMP-dependent protein kinase is activated -> PFK2 is converted to F2,6BPase ->F2,6BP is broken down -> Fructose 1,6-bisphophatase (gluconeogenesis) is activated and PFKl (glycolysis) is inhibited. 

Reflect and Apply How is it possible that both insulin and epinephrine stimulate muscle glycolysis ... 

The control of phosphofructokinase in the liver and in muscle is different. Both epinephrine and glucagon initiate responses to low glucose levels, yet epinephrine stimulates glycolysis in muscle, whereas glucagon inhibits glycolysis in the liver. Explain this fact. 

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