Assessment of the interaction between calmodulin and casein kinase II

Calmodulin is an in vitro substrate for casein kinase II and is also reported to inhibit casein kinase II activity in rat liver nuclear extracts. Here we demonstrate that in the presence or absence of Ca2+, calmodulin did not significantly alter either in vitro casein kinase II activity or autophosphorylation of its beta-subunit. In contrast, Ca2+ inhibited in a dose-dependent manner both casein kinase II activity and casein kinase II-catalysed calmodulin phosphorylation. These data indicate that calmodulin does not directly inhibit casein kinase II activity, but casein kinase II is sensitive to physiologic Ca2+ concentrations.