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Glycogen (black granules) in spermatozoa of a flatworm; transmission electron microscopy, scale: 0.3 μm. Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals, [2] fungi, and bacteria. [3] It is the main storage form of glucose in the human body.
Glycogenesis is the process of glycogen synthesis or the process of converting glucose into glycogen in which glucose molecules are added to chains of glycogen for storage. This process is activated during rest periods following the Cori cycle , in the liver , and also activated by insulin in response to high glucose levels .
Glycogen synthase (UDP-glucose-glycogen glucosyltransferase) is a key enzyme in glycogenesis, the conversion of glucose into glycogen. It is a glycosyltransferase ( EC 2.4.1.11 ) that catalyses the reaction of UDP-glucose and (1,4- α - D -glucosyl) n to yield UDP and (1,4- α - D -glucosyl) n+1 .
The glycogen phosphorylase monomer is a large protein, composed of 842 amino acids with a mass of 97.434 kDa in muscle cells. While the enzyme can exist as an inactive monomer or tetramer, it is biologically active as a dimer of two identical subunits.
Here, 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. [ 1 ] Glucose-1-phosphate is converted to glucose-6-phosphate (which often ends up in glycolysis ) by the enzyme phosphoglucomutase .
Glycogen synthase kinase 3 (GSK-3) is a serine/threonine protein kinase that mediates the addition of phosphate molecules onto serine and threonine amino acid residues. First discovered in 1980 as a regulatory kinase for its namesake, glycogen synthase (GS), [2] GSK-3 has since been identified as a protein kinase for over 100 different proteins in a variety of different pathways.
1,4-alpha-glucan-branching enzyme, also known as brancher enzyme or glycogen-branching enzyme is an enzyme that in humans is encoded by the GBE1 gene. [5] Glycogen branching enzyme is an enzyme that adds branches to the growing glycogen molecule during the synthesis of glycogen, a storage form of glucose. More specifically, during glycogen ...
This enzyme, in turn, activates phosphorylase kinase, which then phosphorylates glycogen phosphorylase b (PYG b), converting it into the active form called phosphorylase a (PYG a). Phosphorylase a is the enzyme responsible for the release of glucose 1-phosphate from glycogen polymers. An example of the pathway would be when glucagon binds to a ...