Glycogen branching enzyme leads to increased osmotic pressure resulting in cellular swelling and death. The tissues most affected by this disease are the liver, heart, and neuromuscular system, areas with the greatest levels of glycogen accumulation. Abnormal glycogen buildup in the liver interferes with liver functioning and can result in an enlarged liver and liver disease. In muscles, the inability of cells to efficiently breakdown glycogen due to the severe reduction or absence of branching can lead to muscle weakness and atrophy. At least three mutations in the GBE1 gene have been found to cause another disease called adult polyglucosan body disease (APBD).
Glycogen phosphorylase presences of AMP. Glycogen phosphorylase Glycogen phosphorylase is one of the phosphorylase enzymes (). Glycogen phosphorylase catalyzes the rate-limiting step in glycogenolysis in animals by releasing glucose-1-phosphate from the terminal alpha-1,4-glycosidic bond. Glycogen phosphorylase is also studied as a model protein regulated by both reversible phosphorylation and allosteric effects. Glycogen phosphorylase breaks up glycogen into glucose subunits (see also figure below): (α-1,4 glycogen chain) + Pi ⇌ (α-1,4 glycogen chain) + α-D-glucose-1-phosphate. Glycogen is left with one fewer glucose molecule, and the free glucose molecule is in the form of glucose-1-phosphate. In order to be used for metabolism, it must