Definition:
Breakdown of Glycogen to Glucose is called Glycogenolysis.
Glycogen stored in the liver and muscle cells of animals, is broken down into glucose to provide immediate energy or to maintain blood glucose levels during times of need.
Glycogenolysis is thus the breakdown of glycogen (n) to glucose-1-phosphate and glycogen (n-1).
Glycogen branches are catabolized by the sequential removal of glucose monomers via phosphorolysis, by the enzyme glycogen phosphorylase.
Location:
Takes place in the cytoplasm of cells in the muscle, liver, and adipose tissue.
Result: Glucose-1-phosphate is released from the non-reducing ends of glycogen chains.
Steps:
Glycogen phosphorylase cleaves the bond linking a terminal glucose residue to a glycogen branch by substitution of a phosphoryl group for the α-[1→4] linkage.
Glucose-1-phosphate is converted to glucose-6-phosphate by the enzyme phosphoglucomutase.
Glucose residues are phosphorylated from branches of glycogen until four residues before a glucose that is branched with a α-[1→6] linkage.
Glycogen debranching enzyme then transfers three of the remaining four glucose units to the end of another glycogen branch.
This exposes the α-[1→6] branching point, which is hydrolyzed by α[1→6] glucosidase, removing the final glucose residue of the branch as a molecule of glucose and eliminating the branch.
This is the only case in which a glycogen metabolite is not glucose-1-phosphate. The glucose is subsequently phosphorylated to glucose-6-phosphate by hexokinase.
Important Enzymes:
Glycogen phosphorylase breaks α-1,4 linkages and debranching enzyme breaks α-1,6 linkages to release single units of glucose-1- phosphate.
Phosphoglucomutase converts glucose- 1-phosphate to glucose-6-phosphate, which is then shuttled into the glycolytic pathway.
Stimulation:
Glucagon (liver) and epinephrine (liver and muscle) stimulate glycogenolysis via the cAMP protein kinase.
Inhibition:
Insulin inhibits glycogenolysis via dephosphorylation and thus results in the inactivation of glycogen phosphorylase.
Commonly Asked Questions.
Write in short about “Glycogenolysis.”.