Glycogen Phosphorylase

Glycogen, a polymer of glucose, is the major storage form for carbohydrates, and serves as a quick energy supply when it is converted to glucose-1-P, thereby stimulating glycolysis and oxidative phosphorylation. Glycogen phosphorylase is a central enzyme in controlling use of the stored glucose molecules. The process is regulated by hormones, via covalent modification of the enzyme by phosphorylation, as well as by normal intracellular effectors that define the energy state of the cell. The homodimeric enzyme has very large subunits, with three separate regulatory sites, plus the site for phosphorylation.