Some characteristics of phosphorylation and dephosphorylation of proteins of isolated rat liver nuclei.

The phosphorylation and dephosphorylation reactions of the proteins of isolated rat liver nuclei were examined in the presence of ATP. It was shown that the plateau value of the phosphorus incorporation at high concentrations of ATP is the result of an equilibrium of phosphorylation and dephosphorylation. The data of 32P-labelling experiments and those of chemical determination of net change of phosphorus content were compared. The activity of an efficient protein phosphatase in rat liver nuclei is demonstrated. It was shown that the pool of protein-phosphorus in the nuclei is heterogeneous as regards its turnover rate. A protein-phosphorus fraction of high turnover dominates the picture of phosphorylation and dephosphorylation reactions when studied with [gamma-32P] ATP in vitro.