Glycogen many respects serves as a countersignal to insulin. In response to insulin levels being below normal (when blood levels of glucose begin to fall below the normal range), glucagon is secreted in increasing amounts and stimulates both glycogenolysis (the breakdown of glycogen) and gluconeogenesis (the production of glucose from other sources). Muscle cell glycogen appears to function as an immediate reserve source of available glucose for muscle cells. Other cells that contain small amounts use it locally, as well. As muscle cells lack glucose-6-phosphatase, which is required to pass glucose into the blood, the glycogen they store is available solely
Glucose 1-phosphate Glucose 1-phosphate Glucose 1-phosphate (also called cori ester) is a glucose molecule with a phosphate group on the 1'-carbon. It can exist in either the α- or β-anomeric form. In glycogenolysis, it is the direct product of the reaction in which glycogen phosphorylase cleaves off a molecule of glucose from a greater glycogen structure. A deficiency muscle glycogen phosphorylase is known as glycogen storage disease type V (McArdle Disease). To be utilized in cellular catabolism it must first be converted to glucose 6-phosphate by the enzyme phosphoglucomutase. One reason that cells form glucose 1-phosphate instead of glucose during glycogen breakdown