Activation of Skeletal Muscle Phosphorylase Kinase by Adenosine Triphosphate and Adenosine 3′,5′-Monophosphate

Rabbit skeletal muscle phosphorylase kinase has been obtained as a nearly homogeneous protein showing a single peak on electrophoresis and in the ultracentrifuge. Incubation of the purified kinase with γ32P-ATP in the presence of Mg++ ions activates the enzyme; this process is accompanied by phosphorylation of the protein. Activation and phosphorylation of phosphorylase kinase occur more rapidly when cyclic 3',5'-AMP or glycogen is present in activation reaction mixtures, but these two substances apparently act by different mechanisms since their effects are additive. Cyclic 3',5'-AMP and glycogen stimulate activation of the kinase more than they affect phosphorylation. No evidence was obtained to indicate that cyclic 3',5'-AMP undergoes any modification when it exerts its effect on phosphorylase kinase activation. Activation of the kinase was shown to be autocatalytic, but the possibility that cyclic 3',5'-AMP acts through stimulation of a second enzyme involved in the system was suggested by the failure to find any evidence for a significant degree of binding of this nucleotide to purified phosphorylase kinase.