Glycogen core a glycogenin protein. Glycogen in muscle, liver, and fat cells is stored in a hydrated form, composed of three or four parts of water per part of glycogen associated with 0.45 millimoles (18 mg) of potassium per gram of glycogen. As a meal containing carbohydrates or protein is eaten and digested, blood glucose levels rise, and the pancreas secretes insulin. Blood glucose from the portal vein enters liver cells (hepatocytes). Insulin acts on the hepatocytes to stimulate the action of several enzymes, including glycogen synthase. Glucose molecules are added to the chains of glycogen as long as both insulin
Glucose 6-phosphatase variety of muscles across the animal kingdom, albeit at very low concentrations. Thus, 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 important role during periods of fasting and when glucose levels are low. It has been shown that starvation and diabetes induces a 2-3-fold increase in glucose-6-phosphatase activity in the liver. Glc 6-Pase activity also increases dramatically at birth when an organism becomes independent of the mothers source of glucose. The human Glc 6-Pase gene contains five exons