Glycogenolysis
353805
212084361
2008-05-13T11:12:15Z
81.156.252.68
/* First step */
{{distinguish|Glycolysis}}
[[Image:Glycogen.png|thumb|[[Glycogen]]]]
[[Image:Glucose-2D-skeletal.png|thumb|[[Glucose]]]]
[[Image:Glucose-6-phosphate-skeletal.png|thumb|[[Glucose-6-phosphate]]]]
'''Glycogenolysis''' (also known as "Glycogenlysis") is the [[catabolism]] of [[glycogen]] by cleavage 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 in humans do not possess glucose-6-phosphatase and hence 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 5 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) The final action of the debranching enzyme leads to the original glucose 1-P connected 1,4 to another branch being released.
===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==
*[http://www2.ufp.pt/~pedros/bq/glycogen.htm#degrada The chemical logic of glycogen degradation at ufp.pt]
*{{MeshName|Glycogenolysis}}
[[Category:Metabolic pathways]]
[[Category:Hepatology]]
{{Carbohydrate metabolism}}
{{Glycogenesis and glycogenolysis}}
[[cs:Glykogenolýza]]
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[[ja:グリコーゲンの分解]]
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