Glycogen àààGlucose-1-phoshateàGlucose-6-phosphate

Gluocse-1-phosphateà UDP-GlucoseàGlycogen

UDP-GlucoseàUDP-GalactoseàUDP-Gluocose

·        Glycogen is broken down into glucose-1-phosphate by the enzyme glycogen phosphorylase.  

·        This enzyme is active when phosphorylated and inactive when dephosphorylated.

·        It can also be activated allosterically (by AMP). AMP is increased in anoxia and activates glycogen phosphorylase without phosphorylating it. 

·        Ca++ will also activate GP.

·        GP is inhibited by ATP (increased in a well fed state when there is plenty of G6P… G6P instead will stimulate production of Glycogen from UDP-Glucose).

·        The enzyme’s phosphorylation is done by Phosphorylase Kinase.

·        Phophorylase Kinase is phosphorylated (activated by Protein Kinase A).

·        Gs receptors are stimulated by hormones like epinephrine (a1, a2, b1, b2) and glucagon (Glucagon receptor in hepatocytes, a Gs membrane receptor).

·        Gs receptor activated (by B1, B2, D1, H2, V2) à Adenylyl cyclase activated à make cAMP out of ATP à cAMP activates Protein Kinase A à PKA then activates Phosphorylase kinase à which then phosphorylates the Glycogen phosphorylase.