BIOL 638 Chapter 15

Structure of glycogen β-granule

* Glycogenin primer = protein primer that serves as a primer for glycogen synthesis.
* Multiple branches (tiers)

Glycogen phosphorylase

* Catalyzes phosphorolytic cleavage of glycogen at non-reducing ends, releases **glucose 1-phosphate**
* Active form (a) is phosphorylated (phosphorylase b kinase)
* Inactive form (b), phosphatase removes phosphate (PP1)
* **Activated in low-energy states**
* Glucagon (liver)
* Epinephrine\[Ca2+\], \[AMP\] (muscle)

Phosphorylase b kinase

Phosphorylates glycogen phosphorylase

Phosphoprotein phosphatase 1 (PP1)

* Regulates the interconversion between GPa and GPb
* Removes Pi from phosphorylase *a*
* Activated by
* Insulin
* Glucose 6-phosphate
* Inhibited by
* Glucagon
* Epinephrine

Glycogen Synthase Kinase 3 (GSK3)

* Cannot function until Casein Kinase II primes glycogen synthase
* Adds phosphoryl groups to 3 Ser residues
* Converts GPb to GPa
* Inhibited by insulin

Glucagon

Stimulates the breakdown of glycogen in the liver

Protein Kinase A (PKA)

* Regulates the activity of glucagon
* Phosphorylates
* Phosphorylase kinase
* Glycogen synthase
* PFK-2/FBPase-2
* Inactivates pyruvate kinase