Glycogenolysis

Glycogenolysis

1. Glycogen Metabolism Usman Saleem RLCP

2. Glycogenolysis Glycogenolysis is the metabolic pathway by which glucose 6-phosphate is produced from glycogen. This process is not simply the reverse of glycogen synthesis (glycogenesis), because it does not require UTP or UDP molecules.

3. Glycogenolysis The Pathway Reaction Steps Glycogen Degradation consists of three steps: R elease of a glucose residue from glycogen, G lycogen remodeling to permit further degradation, and C onversion of glucose 1-phosphate into glucose 6-phosphate for further metabolism .

4. Step 1 Release of a Glucose Residue from Glycogen The enzyme glycogen phosphorylase cleaves a 1-4 glycosidic bond to release glucose unit from the non-reducing end of the glycogen molecule as glucose 1-phosphate.

5. Step 1 Release of a Glucose Residue from Glycogen

6. Step 2 Glycogen Remodeling to Permit Further Degradation Glycogen phosphorylase sequentially remove glucose units from the non-reducing ends of all chains, stopping four residues from a -(1,6) branch point.  The a -1,6-glycosidic bonds at the branch points are not susceptible to cleavage by phosphorylase

7. Step 2 Glycogen Remodeling to Permit Further Degradation Two additional enzymes (transferase and a -1,6-Glucosidase) remodel the glycogen for continued degradation by phosphorylase. The transferase shifts a block of three glycosyl residues from one outer branch to the non-reducing end of the linear chain.   This transfer exposes a single glucose residue joined by an a -1,6-glycosidic linkage.

8. Step 2 Glycogen Remodeling to Permit Further Degradation a -1,6-Glucosidase , also known as the debranching enzyme , hydrolyzes the a -1,6-glycosidic bond, resulting in the release of a free glucose molecule .

9. Step 3 Conversion of glucose 1-phosphate into glucose 6-phosphate for further metabolism In the debranching reaction, the enzyme phosphoglucomutase catalyzes the isomerization of glucose 1-phopsphate to glucose 6-phosphate.

10. Step 3 Conversion of glucose 1-phosphate into glucose 6-phosphate for further metabolism

11. Fate of G6P derived from Glycogenolysis The fate of the glucose 6-phosphate derived from Glycogenolysis differ in liver and muscle. Liver contains the enzyme glucose 6-phosphatase which converts the glucose 6-phosphate to free glucose , which helps to maintain the blood glucose concentration in the fasting state.

12. Fate of G6P derived from Glycogenolysis During glycogen degradation in muscle, the main aim is to produce energy quickly and so the glucose 6-phosphate is metabolized immediately via glycolysis. This tissue does not contain glucose 6-phosphatase.

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