Glycogenolysis

From Citizendium, the Citizens' Compendium
Jump to: navigation, search
This article is basically copied from an external source and has not been approved.
Main Article
Talk
Related Articles  [?]
Bibliography  [?]
External Links  [?]
Citable Version  [?]
 
This editable Main Article is under development and not meant to be cited; by editing it you can help to improve it towards a future approved, citable version. These unapproved articles are subject to a disclaimer.
The content on this page originated on Wikipedia and is yet to be significantly improved. Contributors are invited to replace and add material to make this an original article.

Glycogenolysis is the catabolism of glycogen by removal of a glucose monomer through reaction with phosphate to produce glucose-1-phosphate. This derivative of glucose is then converted to glucose 6-phosphate, a key intermediate in glycolysis. The hormones glucagon and epinephrine stimulate glycogenolysis.

Glycogenolysis requires three enzymes :

  • Glycogen phosphorylase (breaks down glucose polymer at α-1-4 linkages, yielding glucose-1-phosphate and a shorter glycogen molecule)
  • Debranching enzyme transferase / α-1,6-Glucosidase (bifunctional enzyme) (transfers α-1-6-linked glucose to end of glycogen chain for glycogen phosphorylase, and removes the glucose present at the branching point as free glucose)
  • Phosphoglucomutase (converts glucose-1-phosphate to glucose-6-phosphate)

Glycogenolysis occurs 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. Since muscle cells lack glucose 6-phosphatase, they cannot convert glucose-6-P into glucose, and therefore use the glucose-6-phosphate for their own energy demands. However, since the glucose residues present as the branching points of the glycogen molecule are removed as free glucose (rather than as glucose-6-phosphate), even muscle cells are able to release a small amount of glucose into the bloodstream.

Perenteral administration of glucagon is a common human medical intervention in diabetic emergencies when sugar cannot be given orally.

External links