[Effect of ATP, ADP and magnesium ions on the activity of phosphorylase kinase from rabbit skeletal muscles].

The dependence of enzymatic activity of phosphorylase kinase on ATP and magnesium concentrations has been studied. The enzyme activity has been shown to be inhibited by the substrate surplus (Mg-ATP) but free Mg2+ stimulates the enzyme. At saturating concentrations of ATP the activating effect of Mg2+ is maximum at the Mg/ATP ratio of 6-10. The ADP inhibition action is characterized by an incompetitive type towards ATP. The apparent Ki value is equal to 0.2 mM. It is suggested that the specific ADP-binding site spatially removed from the active site has an importance for the phosphorylase kinase activity regulation.