Both 49 K and 60 K subunits of brain Ca2+-calmodulin-dependent protein kinase (calmodulin-kinase) were autophosphorylated in a Ca2+-calmodulin-dependent manner with changes in apparent molecular weights to 53 K and 64 K on SDS-PAGE. The amounts of phosphate incorporated into the 49 K and 60 K subunits were 6.5 and 15.7 mol per mol subunit, respectively, on 5-min incubation. Protein phosphatase C from bovine brain dephosphorylated calmodulin-kinase with concomitant restoration of original molecular weights on SDS-PAGE. Inhibitor-2, an inhibitor protein for protein phosphatase 1, inhibited the dephosphorylation of the kinase by protein phosphatase C only by 10-20%, indicating that both protein phosphatases 1 and 2A are involved in the reaction. These results suggest that the calmodulin-kinase activity is regulated by the phosphorylation and dephosphorylation of the enzyme itself.
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