Staurosporine: An Effective Inhibitor for Ca2+/Calmodulin‐Dependent Protein Kinase II

: We investigated the effect of staurosporine on Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) purified from rat brain. (a) Staurosporine (10–100 nM) inhibited the activity of CaM kinase II. The half-maximal and maximal inhibitory concentrations were 20 and 100 nM, respectively. (b) The inhibition with staurosporine was of the noncompetitive type with respect to ATP, calmodulin, and phosphate acceptor (β-casein). (c) Staurosporine suppressed the autophosphorylation of α- and β-subunits of CaM kinase II at concentrations similar to those at which the enzyme activity was inhibited. (d) Staurosporine also attenuated the Ca2+ calmodulin-independent activity of the autophosphorylated CaM kinase II. These results suggest that staurosporine inhibits CaM kinase II by interacting with the catalytic domain, distinct from the ATP-binding site or substrate-binding site, of the enzyme and that staurosporine is an effective inhibitor for CaM kinase II in the cell system.