pathway
Last reviewed 01/2018
The first stage in glycogenesis is provision of precursor glucose; this is dependent on site:
- in skeletal muscle:
- take up glucose from plasma
- minimal contribution from direct conversion of lactate to glucose within muscle; normally the lactate produced during anaerobic glycolysis diffuses out of the cell and is transported to the liver where glucose is reformed by gluconeogenesis
- in liver:
- absorb glucose from portal blood, particularly after meal
- glyconeogenesis
The pathway is then similar:
- hexokinase in muscle, or glucokinase in liver, phosphorylate glucose to glucose-6-phosphate
- phosphoglucomutase converts glucose-6-phosphate to glucose-1-phosphate
- glucose-1-phosphate uridyltransferase converts glucose-1-phosphate and uridyl triphosphate into uridyl diphospate glucose (UDP glucose) and pyrophosphate
- glycogen synthase converts UDP glucose and glycogen(n residues) into UDP and glycogen(n+1 residues)
In addition, there are enzymes which:
- create primer sequences that initiate glycogen formation
- create a branching structure to the growing glycogen chain e.g. 1,6-alpha-glucosyltransferase