Glycogen Phosphorylase:
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.