Part VI. Regulating the Glycogenolysis Cascade

The glycogenolysis cascade is regulated by the intracellular levels of cAMP. When the levels of cAMP is high, not only does cAMP activate glycogen degradation and inhibit glycogen synthesis, there is a further brake applied on glycogen synthesis. At high cAMP levels, cAPK phosphorylates an inhibitor of phosphoprotein phosphatase. This inhibitor binds to phosphoprotein phosphatase and inactivates it.

When the level of cAMP in the cell is low, the phosphoprotein phosphatase inhibitor is not phosphorylated and consequently is not bound to phosphoprotein phosphatase. This allows the phosphatase to remove the phosphoryl group from glycogen synthase thereby activating it and stimulating glycogen synthesis. Phosphoprotein phosphatase also removes the phosphoryl groups from glycogen phosphorylase kinase as well as glycogen phosphorylase which inactivates these enzymes and prevents glycogen from being degradated.

The entire pathway is shown here.