Proteolysis activated protein kinase in Dictyostelium discoideum

In the search for MBP phosphorylating activities in Dictyostelium discoideum, we have found a proteolysis-activated protein kinase. This activity which is distributed between the soluble and the particulate fractions of the cell, uses MBP and histone as substrate and has a molecular mass of 140 kDa as detected in an 'in situ' assay. This protein kinase has several features shared by the protein kinase C family, such as substrate specificity and sensitivity to proteolysis, but its molecular mass is much larger than that described for the known protein kinase C isoforms. To better characterize this activity we have studied its sensitivity to several protein kinase C inhibitors and activators. This protein kinase is activated neither by phorbol ester nor by phosphatidylserine or Ca2+. The activity is inhibited by staurosporine and PKC zeta pseudosubstrate, but is not affected by the specific protein kinase C inhibitor bisindolylmaleimide. These data lead us to propose that proteolytically activated Dictyostelium protein kinase belongs to the recently described protein kinase C-related family.