INACTIVATION AND SELF-ASSOCIATION OF CA2-DEPENDENT PROTEIN-KINASE-II DURING AUTOPHOSPHORYLATION( CALMODULIN)

The time-dependent loss in enzyme activity associated with the autopho sphorylation of Ca2+/calmodulin-dependent protein kinase II (CaM-kinas e) was altered by both pH and ATP concentration, These parameters also influenced the extent to which soluble CaM-kinase undergoes self-asso ciation to form large aggregates of sedimentable enzyme, Specifically, autophosphorylation of CaM-kinase in 0.01 mM ATP at pH 6.5 resulted i n the formation of sedimentable enzyme and a 70% loss of enzyme activi ty, Under similar conditions at pH 7.5, the enzyme lost only 30% of it s activity, and no sedimentable enzyme was detected, In contrast to 0. 01 mM ATP, autophosphorylation of CaM-kinase at pH 6.5 in 1 mM ATP did not result in a loss of activity or the production of sedimentable en zyme, even though the stoichiometry of autophosphorylation was compara ble, Electron microscopy studies of CaM-kinase autophosphorylated at p H 6.5 in 0.01 mM ATP revealed particles 100-300 nm in diameter that cl ustered into branched complexes. Inactivation and self-association of CaM-kinase were influenced by the conditions of autophosphorylation in vitro, suggesting that both the catalytic and physical properties of the enzyme may be sensitive to fluctuations in ATP concentration and p H in vivo.