Dictionary:
gly·co·gen·ol·y·sis (glī'kə-jə-nŏl'ĭ-sĭs) ![]() |
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| Chemistry Dictionary: glycogenolysis |
The conversion of glycogen to glucose, which occurs in the liver and is stimulated by glucagon from the pancreas and adrenaline from the adrenal medulla. These hormones activate an enzyme that phosphorylates glucose molecules in the glycogen chain to form glucose 1-phosphate, which is converted to glucose 6-phosphate. This is then converted to glucose by a phosphatase enzyme. In skeletal muscle glycogen is degraded to glucose 6-phosphate, which is then converted into pyruvate and used in ATP production during glycolysis and the Krebs cycle. However, pyruvate can also be converted, in the liver, to glucose; thus muscle glycogen is indirectly a source of blood glucose. Compare glycogenesis.
| Food and Nutrition: glycogenolysis |
The breakdown of glycogen to glucose for use as a metabolic fuel and to maintain the normal blood concentration of glucose in the fasting state. Stimulated by the hormones glucagon and adrenaline.
| Dental Dictionary: glycogenolysis |
The formation of blood glucose by hydrolysis of stored liver glycogen.
| Sports Science and Medicine: glycogenolysis |
The breakdown of glycogen to form glucose. See also glucagon.
| Veterinary Dictionary: glycogenolysis |
The splitting up of glycogen in the liver or muscle, yielding glucose-1-phosphate.
| Wikipedia: Glycogenolysis |
Glycogenolysis (also known as "Glycogenlysis") is the catabolism of glycogen by removal of a glucose monomer through cleavage with inorganic phosphate to produce glucose-1-phosphate.[1] This derivative of glucose is then converted to glucose-6-phosphate, an intermediate in glycolysis.
The hormones glucagon and epinephrine stimulate glycogenolysis.
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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 produced in the Alpha cells of the Islets of Langerhans.
Parenteral (intravenous) administration of glucagon is a common human medical intervention in diabetic emergencies when sugar cannot be given orally. It can also be administered intramuscularly.
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 4 linked glucoses are left on the branch. (, glycogen phosphorylase (EC 2.4.1.1) can be used as a marker enzyme to determine glycogen breakdown. )
The 2nd step involves the debranching enzyme that moves three remaining glucose units to another 1,4 end of glycogen. The final action of the debranching enzyme is the hydrolysis of the glucose attached as a 1,6-branched, giving one free glucose. This is the only case in which glucose-1-phosphate is not a glycogen metabolite.
The 3rd and last stage converts G1P (glucose-1-phosphate) to G6P (glucose-6-phosphate) through the enzyme phosphoglucomutase.
The key regulatory enzyme of the process of glycogenolysis is glycogen phosphorylase:
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