Protein kinases in hepatoma, and adult and fetal liver of the rat. I. Subcellular distribution.

Comparison of the subcellular distribution of protein kinases in hepatoma, adult and fetal liver showed that nuclei of growing tissues contain a 3 to 5 times higher percentage of the activity in whole homogenate than nuclei of adult liver. The cytoplasmic protein kinase in hepatoma and fetal liver was stimulated by cAMP⁷ only half as much as that in adult liver. The nuclear activity was unresponsive to cAMP in all three tissues. Subfractionation of nuclei gave a final preparation that was more active with endogenous substrate than with added histone as phosphate acceptor. The hepatoma nuclei contained latent activity that could be unmasked in the presence of Triton X-100, those of adult and fetal liver did not. A partial resolution of the nuclear activity on DEAE-cellulose is reported.