Glycogenolysis: Glycogen Breakdown
Glycogenolysis is the breakdown of glycogen into glucose-1-phosphate and glucose, providing immediate energy or maintaining blood glucose levels.
| Enzyme | Function |
|---|---|
| Glycogen Phosphorylase | Rate-limiting step; cleaves $\alpha$-1,4-glycosidic bonds to release glucose-1-phosphate. Requires Vitamin B6. |
| Debranching Enzyme | Moves branches and removes the single glucose residue at the $\alpha$-1,6-linkage. |
| Phosphoglucomutase | Converts glucose-1-phosphate to glucose-6-phosphate (which then enters glycolysis or blood). |
High-Yield Core Realities:
- Hormonal Regulation: Glucagon (liver) and Epinephrine (muscle/liver) activate glycogen phosphorylase via the cAMP/protein kinase A pathway.
- Tissue Specificity: Only the liver expresses Glucose-6-phosphatase, allowing it to release free glucose into the blood. Muscles lack this enzyme, so they use glucose-6-phosphate locally for energy.
- Clinical Correlate: Glycogen Storage Diseases (GSDs) involve defects in these enzymes (e.g., Von Gierke disease is a deficiency in Glucose-6-phosphatase).