The Relationship of Epinephrine and Glucagon to Liver Phosphorylase

The concentration of phosphorylase in liver slices changes rapidly in response to certain experimental conditions (14). The concentration of phosphorylase in the cells represents a balance between inactivation of the enzyme and reactivation to the active form. Inactivation of liver phosphorylase is catalyzed by an enzyme formerly designated liver phosphorylase-inactivating enzyme. The synthetic aspect of the balance, i.e. the reactivation of the inactive liver phosphorylase, is influenced by epinephrine and glucagon so that resynthesis of the active form is promoted (5). The experiments reported in t,he following papers were designed to aid our understanding of the mechanisms involved in the regulation of the concentration of liver phosphorylase in intact cells. Liver phosphorylase and the enzyme from liver which inactivates it have been prepared in purified form. The enzymatic inactivation of liver phosphorylase has been studied (6) and also the process of reactivation in slices and extracts (5). This report deals with the preparation and properties of liver phosphorylase. Two major problems required solution. The enzymatic inactivation of liver phosphorylase proceeds rapidly unless precautions are taken. Consequently, the early steps have been designed primarily to inhibit, denature, or remove the liver phosphorylase-inactivating enzyme. The second problem was created by the tendency of liver phosphorylase to accompany glycogen during fractionation. As purification proceeded, the ratio of carbohydrate to protein increased to values of 20 or 30 to 1, and, therefore, steps were taken to lower the glycogen concentration of the preparation. The procedures described here have resulted in greater yields of enzyme with a higher specific activity than reported previously, even though apparently homogeneous preparations of liver phosphorylase were obtained by an earlier procedure (7).