Glycogenolysis (also known as "Glycogenlysis") is the
catabolismof glycogenby removal of a glucosemonomer through cleavage with inorganic phosphateto produce glucose-1-phosphate. This derivative of glucose is then converted to glucose-6-phosphate, an intermediate in glycolysis.
glucagonand epinephrinestimulate glycogenolysis.
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 glucoseconcentrations.
Liver(hepatic) cells can consume the glucose-6-phosphate in glycolysis, or remove the phosphate group using the enzyme glucose-6-phosphataseand release the free glucose into the bloodstream for uptake by other cells.
Musclecells in humans do not possess glucose-6-phosphatase and hence will not release glucose, but instead use the glucose-6-phosphate in glycolysis.
intravenous) administration of glucagon is a common human medical intervention in diabetic emergencies when sugar cannot be given orally.
The overall reaction for the 1st step is:
Glycogen (n residues) + Pi <-----> Glycogen (n-1 residues)+ G1P
glycogen phosphorylasecleaves the bond at the 1 position by substitution of a phosphoryl group. It breaks down glucose polymer at α-1-4 linkages until 5 linked glucoses are left on the branch. (Furthermore, glycogen phosphorylase(EC 184.108.40.206) can be used as a marker enzyme to determine glycogen breakdown. )
The 2nd step involves the
debranching enzymethat moves the remaining glucose units to another non-reducing end. This results in more glucose units available to glycogen phosphorylase. (step 1) The final action of the debranching enzyme leads to the original glucose 1-P connected 1,4 to another branch being released.
The 3rd and last stage converts G1P (glucose-1-phosphate) to G6P (glucose-6-phosphate) through the enzyme
The key regulatory enzyme of the process of glycogenolysis is Glycogen phosphorylase:
* Phosphorylation --> activation
* Dephosphorylation --> inhibition
* [http://www2.ufp.pt/~pedros/bq/glycogen.htm#degrada The chemical logic of glycogen degradation at ufp.pt]
Wikimedia Foundation. 2010.