INCREASED ACTIVITY OF THE EEF-2 SPECIFIC, CA2+ AND CALMODULIN DEPENDENT PROTEIN-KINASE III DURING THE S-PHASE IN EHRLICH ASCITES-CELLS

The activity of the eukaryotic elongation factor (eEF-2) specific, Ca2+ and calmodulin dependent protein kinase III (CaM PK III) was studied in homogenated Ehrlich ascites tumour cells. The eEF-2 kinase activity was determined in the presence of an excess of the substrate, i.e., non-limiting concentrations of eEF-2. The homogenates showed both kinase and phosphatase activity. The latter activity was inhibited by the protein phosphatase 2A inhibitor okadaic acid. Analysis of the kinase using cells from defined stages of the cell cycle showed that the highest activity was found in cells from the early S-phase, whereas the phosphatase activity was most pronounced during the G2+M phase. © 1991 Academic Press, Inc.