Interaction (glycogen synthase and glycogen phosphorylase)

Precise details of the structure and its relation to regulation of both enzymes is given in the submenu. The essential points are:

• glycogen phosphorylase releases glucose from glycogen
• glycogen synthase catalyzes the reverse reaction
• both enzymes are present in the liver and skeletal muscle
• both are subject to regulation by secondary messenger cascades which result in varying concentrations of mediators such as cAMP and calcium
• the mediators affect a number of enzymes which change the degree of phosphorylation of both enzymes; the key difference is that glycogen phosphorylase is activated by phosphorylation whereas glycogen synthase is inactivated by phosphorylation
• additionally, there are subtle variations in responsiveness between the enzyme cycles in the liver and skeletal muscle e.g. the liver is more influenced by the plasma glucose concentration and has receptors for glucagon