Muscle glycogen stores can NOT be used to provide glucose into the circulation due to lack of:
Glucose 6-phosphataseIt is an enzyme that hydrolyzes glucose-6-phosphate resulting in the creation of a phosphate group and free glucose.Glucose is then expoed from the cell glucose transpoer membrane proteins.This catalysis completes the final step in gluconeogenesis and glycogenolysis and therefore plays a key role in the homeostatic regulation of blood glucose levels.In humans, there are three isozymes, G6PC, G6PC2, and G6PC3.Genes coding for the enzyme are primarily expressed in the liver, in the kidney coex and (to a lesser extent) in the beta-cells of the pancreatic islets and intestinal mucosa (especially during times of starvation).The glycogen that muscles store is not usually available for the rest of the body's cells because glucose-6-phosphate cannot cross the sarcolemma unless it is dephosphorylated.The enzyme plays an impoant role during periods of fasting and when glucose levels are low.
Glucose-6-phosphate dehydrogenase
Glutamate dehydrogenase
Glucose-6-phosphatase
Glucokinase