Phosphorylase kinase: development of a continuous fluorometric assay for the determination of catalytic activity

The preferential binding of 1-anilinonaphthalene-8-sulfonate by rabbit muscle phosphorylase a is the basis of a continuous fluorometric assay for phosphorylase kinase. The maximum rate of change in fluorescence (d delta F/dt) is dependent on both the concentration of phosphorylase kinase and on conditions, such as pH and calcium ion concentration, which affect the enzyme. Parallel measurements of the increases in fluorescence and of 32P incorporation demonstrate the existence of a distinct intermediate in the conversion of phosphorylase b to a. We have used the assay to monitor the increase in calcium-independent activity which accompanies the limited chymotryptic digestion of phosphorylase kinase.