Glycogenolysis

Glycogenolysis is the catabolism of glycogen by removal of a glucose monomer and addition of phosphate to produce glucose-1-phosphate. This derivative of glucose is then converted to glucose-6-phosphate, a potent 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)
• Debranching enzyme transferase / α-1,6-Glucosidase (bifunctional enzyme) (transfers α-1-6-linked glucose to end of glycogen chain for glycogen phosphorylase)
• Phosphoglucomutase (converts glucose-1-phosphate to glucose-6-phosphate)

Furthermore, glycogen phosphorylase (EC 2.4.1.1) can be used as a marker enzyme to determine glycogen breakdown.

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.

Parenteral (IV) administration of glucagon is a common human medical intervention in diabetic emergencies when sugar cannot be given orally.

External links

• The chemical logic of glycogen degradation

Transferase enzyme = Oligoglycan transferase