Question

How do the two enzymes, phosphorylase kinase and phosphoprotein phosphatase, work together to regulate the glycogen phosphorylase enzyme?

Answer 1

Ans. Glycogen phosphorylase catalyzes breakdown of glycogen into Glucose - 1- phosphate.

Glycogen phosphorylase uses phosphate instead of water to break down glycogen. Glycogen phosphorylase manages to use phosphate to catalyze glycogen breakdown by employing the coenzyme pyridoxal phosphate.

Regulation of Glycogen Phosphorylase enzyme :-

In muscle, glycogen phosphorylase exists as a usually active form( GPa) and an inactive form (GPb). Both GPa and GPb differ chemically only in that GPa is phosphorylated ( two phosphates) , but GPb is not. GPb is converted to GPa by phosphorylation by an enzyme known as phosphorylase kinase.

Turning off Glycogen breakdown :-

The steps in the glycogen breakdown regulatory pathway can be reversed at several levels. First, the ligand can leave the receptor. Second, the G proteins have an inherent GTPase activity that serves to turn them off over time. Third, cells have phosphodiesterase for breaking down cAMP. Fourth, an enzyme known as protein phosphatase ( also called phosphoprotein phosphatase) can remove phosphates from phosphorylase kinase (inactivating it) and from GPa, converting it to the much less active GPb.