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 &alpha;-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]] [[da:Glykogenolyse]] [[de:Glykogenolyse]] [[fr:Glycogénolyse]] [[it:Glicogenolisi]] [[ms:Glikogenolisis]] [[nl:Glycogenolyse]] [[ja:グリコーゲンの分解]] [[oc:Glicogenolisi]] [[pt:Glicogenólise]] [[sv:Glykogenolys]]