1. Glycogen Metabolism
Reducing end

2. Glycogen Metabolism
Glycogen Breakdown (Glycogenolysis) and Glycogen Synthesis
Why breakdown glycogen and not lipid to produce glc?
1. Mobilized faster
2. Can be metabolized anaerobically
Glycogen breakdown
Glc units are removed one at a time from the nonreducing ends by phosphorolysis

3. Glycogen Metabolism Glycogen Breakdown
Remove all the 14 branches and an additional enzyme is rec’d to remove 16

4. Glycogen Metabolism Glycogen Breakdown - Glycogen phosphorylase
First known example of an allosterically regulated enzyme
First enzyme shown to be controlled by reversible phosphorylation
In muscle:
Resting muscle
During vigorous muscular activity, epinephrine triggers phos
Triggers glycogen breakdown

5. Glycogen Metabolism Glycogen Breakdown - Glycogen phosphorylase
In liver:
phosphorylase kinase
Low blood sugar - glucagon activates phosphorylase b kinase, initiates release of glc into blood

6. Glycogen Metabolism Glycogen Breakdown Fate of glucose 1-phosphate
Muscle / liver
phosphoglucomutase
G1P  G6P  Glycolysis
If you just need glucose:
Liver
Gluconeogenesis or
glucose 6-phosphatase
Glycogen  G1P  G6P + H2O  Glc + Pi
In brain & muscle:
No gluconeogenesis and no glucose 6-phosphatase so
get glc from gluconeogenesis in liver or from injested glc, both of which get delivered through bloodstream
In liver, glycogen is a reservoir of glc, converted into blood glc that moves to other tissues
In muscle, glycogen breakdown produces glc that is metabolized via glycolysis to provide ATP for muscle contraction

7. Glycogen Metabolism Glycogen Synthesis
Want to polymerize glc, need an activated form of glc - UDP-glucose
Occurs in almost all tissues, especially in liver and muscle
UDP-glucose
pyrophosphorylase
Glycogen
chain
Glycogen synthase
UDP
Glycogen chain + one more glucose residue

8. Glycogen Metabolism
Glycogen Synthesis

9. Glycogen Metabolism
Glycogen Synthesis

10. Glycogen Metabolism Glycogen Synthesis
Glycogen synthase cannot initiate a chain - it needs a primer
Protein enzyme glycogenin makes the primer
Once 8 glucose molecules have been added, Glycogenin-[glc]8 is a substrate for glycogen synthase

11. Glycogen Metabolism Glycogen Synthesis
Glycogen synthase cannot make the (16) bonds found at branches, these are formed by branching enzymes

12. Glycogen Metabolism Glycogen Synthesis
Glycogen synthase cannot make the (16) bonds found at branches, these are formed by branching enzymes

13. Glycogen Metabolism Control
Hormones reciprocally regulate synthesis and degradation by controlling the phosphorylation/dephosphorylation of the key enzymes

14. Glycogen Metabolism Control
Hormones reciprocally regulate synthesis and degradation by controlling the phosphorylation/dephosphorylation of the key enzymes
Glucagon, epinephrine: stimulate phosphorylase
inhibit synthase
Insulin: inhibit phosphorylase
stmulate synthase
(+)
Insulin
(+) Glucagon, epinephrine

15. Glycogen Metabolism Control
Hormones reciprocally regulate synthesis and degradation by controlling the phosphorylation/dephosphorylation of the key enzymes
Glucagon, epinephrine: stimulate phosphorylase & inhibit synthase
Insulin: inhibit phosphorylase & stimulate synthase

16. Glycogen Metabolism

17. Glycogen Metabolism

18. Glycogen Metabolism

19. Glycogen Metabolism