Glycogen synthase expression of the muscle isozyme and not the liver isozyme. However, muscle-specific glycogen synthase activation may lead to excessive accumulation of glycogen, leading to damage in the heart and central nervous system following ischemic insults. The reaction is highly regulated by allosteric effectors such as glucose-6-phosphate (activator) and by phosphorylation reactions (deactivating). Glucose-6-phosphate allosteric activating action allows glycogen synthase to operate as a glucose-6-phosphate sensor. The inactivating phosphorylation is triggered by the hormone glucagon, which is secreted by the pancreas in response to decreased blood glucose levels. The enzyme also cleaves the ester bond between the C1 position of glucose
Glycogen branching enzyme position to which they are transferred, the enzyme creates the very characteristic, highly branched glycogen molecule. Mutations in this gene are associated with glycogen storage disease type IV (also known as Andersen's disease) in newborns and with adult polyglucosan body disease. Approximately 40 mutations in the GBE1 gene, most resulting in a point mutation in the glycogen branching enzyme, have led to the early childhood disorder, glycogen storage disease type IV (GSD IV). This disease is characterized by a severe depletion or complete absence of GBE, resulting in the accumulation of abnormally structured glycogen, known as polyglucosan bodies. Glycogen buildup