Glycogenolysis
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Glycogenolysis is the catabolism of glycogen by removal of a glucose monomer through cleavage with inorganic phosphate to produce glucose-1-phosphate. This derivative of glucose is then converted to glucose-6-phosphate, an intermediate in glycolysis.
The hormones glucagon and epinephrine stimulate glycogenolysis.
Function
Glycogenolysis transpires in the muscle and liver tissue, where glycogen is stored, as a hormonal response to epinephrine (e.g., adrenergic stimulation) and/or glucagon, a pancreatic peptide triggered by low blood glucose concentrations.
- Liver (hepatic) cells can consume the glucose-6-phosphate in glycolysis, or remove the phosphate group using the enzyme glucose-6-phosphatase and release the free glucose into the bloodstream for uptake by other cells.
- Muscle cells will not release glucose, but instead use the glucose-6-phosphate in glycolysis.
Clinical significance
Parenteral (intravenous) administration of glucagon is a common human medical intervention in diabetic emergencies when sugar cannot be given orally.
Reaction
First step
The overall reaction for the 1st step is:
Glycogen (n residues) + Pi <-----> Glycogen (n-1 residues)+ G1P
Here, glycogen phosphorylase cleaves the bond at the 1 position by substitution of a phosphoryl group. It breaks down glucose polymer at α-1-4 linkages until 4 linked glucoses are left on the branch. (Furthermore, glycogen phosphorylase (EC 2.4.1.1) can be used as a marker enzyme to determine glycogen breakdown. )
Second step
The 2nd step involves the debranching enzyme that moves the remaining glucose units to another non-reducing end. This results in more glucose units available to glycogen phosphorylase (step 1)
Third step
The 3rd and last stage converts G1P (glucose-1-phosphate) to G6P (glucose-6-phosphate) through the enzyme phosphoglucomutase.
Regulation
The key regulatory enzyme of the process of glycogenolysis is Glycogen phosphorylase:
- Phosphorylation --> activation
- Dephosphorylation --> inhibition
External links
Metabolism: carbohydrate metabolism - glycogenesis and glycogenolysis enzymes | |
|---|---|
| Glycogenesis | Phosphoglucomutase - UDP-glucose pyrophosphorylase - Glycogen synthase (Glycogen branching enzyme) |
| Glycogenolysis | Glycogen phosphorylase (Debranching enzyme) - Phosphoglucomutase - Glycogenin Maltase |
| Regulation | Phosphorylase kinase - Phosphoprotein phosphatase |
da:Glykogenolyse fr:Glycogénolyse it:Glicogenolisi nl:Glycogenolysesv:Glykogenolys
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
