Autoactivation of calmodulin-dependent protein kinase II by autophosphorylation.
Autophosphorylation of calmodulin (CaM)-dependent protein kinase II (CaM-kinase II) under limiting conditions (2 microM ATP) decreased progressively with increasing concentrations of a substrate, Pro-Leu-Ala-Arg-Thr-Leu-Ser-Val-Ala-Gly-Leu-Pro-Gly-Lys-Lys (syntide-2), suggesting a competition between the substrate and the autophosphorylation site(s) of the enzyme. The rate and extent of the generation of Ca2+/CaM-independent activity of the enzyme by autophosphorylation were also decreased by the presence of syntide-2. The syntide-2 phosphorylation in the presence of Ca2+/CaM under the limiting conditions reached a steady state, after a lag, when the Ca2+/CaM-independent activity reached a plateau. A linear relationship was observed between the activities in the presence and absence of Ca2+/CaM of the enzyme which had undergone various degrees of autophosphorylation, and the extrapolation of activity in the absence of Ca2+/CaM to zero gave 15-20% of the maximum activity. The steady-state rate of syntide-2 phosphorylation in the presence of Ca2+/CaM by the enzyme that had not undergone prior autophosphorylation was decreased by high concentrations of syntide-2 which suppressed autophosphorylation as well as the generation of Ca2+/CaM-independent activity. These results suggest that although the nonautophosphorylated enzyme possesses a basal low level of Ca2+/CaM-dependent activity, autophosphorylation is required for full activation.
Katoh
T
T
Department of Biochemistry, Asahikawa Medical College, Japan.
Fujisawa
H
H
D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011494:Protein Kinases / Q000378:metabolism*
D002147:Calmodulin; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; C063391:syntide-2; D011494:Protein Kinases; D002118:Calcium