[Protein kinase activity in proliferating Ehrlich ascites tumor cells]

It was demonstrated that the activity of cAMP-dependent histone and casein kinases is maximal at the end of the exponential phase of tumour growth, i. e., on the 8-10th day and decreases in the stationary growth phase, i. e., by the 15th day. The maximal activity of histone and casein kinases is observed in the S-phase of the cell cycle, the degree of cAMP-dependent histone kinase activation reaching its maximum. A chromatographic analysis of cytosolic protein kinases revealed a significant increase in the activity of cAMP-dependent histone kinase of the second type within the same time interval. Cell proliferation was paralleled with changes in the relative content of the two forms of casein kinases.