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.
TABLE OF CONTENTS