The major factor which controls glycogen metabolism in the liver is the concentration of phorphorylase alpha. Certainly, this enzyme catalyzes the limiting step of glycogen breakdown and by controlling the activity of synthetase phosphatase, also regulates glycogen synthesis. The configuration of phosphorylase alpha is stimulated by cAMP, By glycogen and presumably also by some still ill-defined ionic changes. The ininactivation of phosphorylase is really stimulated by glucose and inhibited by glycogen and AMP.