A tentative mechanism of the ternary complex formation between phosphorylase kinase, glycogen phosphorylase b and glycogen

The kinetics of rabbit skeletal muscle phosphorylase kinase interaction with glycogen has been studied. At pH 6.8 the binding of phosphorylase kinase to glycogen proceeds only in the presence of Mg2+, whereas at pH 8.2 formation of the complex occurs even in the absence of Mg2+. On the other hand, the interaction of phosphorylase kinase with glycogen requires Ca2+ at both pH values. The initial rate of the complex formation is proportional to the enzyme and glycogen concentrations, suggesting the formation of the complex with stoichiometry 1:1 at the initial step of phosphorylase kinase binding by glycogen. According to the kinetic and sedimentation data, the substrate of the phosphorylase kinase reaction, glycogen phosphorylase b, favors the binding of phosphorylase kinase with glycogen. We suggest a model for the ordered binding of phosphorylase b and phosphorylase kinase to the glycogen particle that explains the increase in the tightness of phosphorylase kinase binding with glycogen in the presence of phosphorylase b.