Purification of a soluble casein kinase II from Dictyostelium discoideum lacking the beta subunit: regulation during proliferation and differentiation.

A type II casein kinase has been purified from the soluble fraction of Dictyostelium discoideum vegetative cells. The enzyme has been purified 370 fold and behaves catalytically as casein kinase type II, in the sense that it utilizes GTP as well as ATP as phosphoryl donors, it is inhibited by low heparin concentrations and phosphorylates a specific peptide for CK II. It is a tetramer of 38 kDa-subunits with catalytic activity and ability to autophosphorylate in vitro. The comparison of this activity with the nuclear enzyme previously purified from the same organism indicates that both have the same molecular structure. Both enzymes have antigenic determinants in common with casein kinase II from bovine thymus, suggesting a high degree of conservation during evolution. Studies on the activity of this enzyme during early differentiation, and in the transition from quiescence to proliferation shows an increase in specific activity suggesting a crucial role for the enzyme in this organism.