Studies on the Intracellular Distribution of Thymidine Phosphorylating Kinase Activities in Regenerating Rat Liver

The intracellular distribution of thymidine phosphorylating kinases has been studied in rat liver at different times after partial hepatectomy. After conventional fractionation in 0.25 M sucrose, thymidine kinase is present in all fractions, the highest proportion being found, however, in the supernatant; phosphorylation of thymidine to TDP and TTP is detected only in the supernatant fraction from 24 h onwards after hepatectomy. Nuclei prepared in 2.2 M sucrose or in non‐aqueous media have the same level of thymidine kinase activity and can never phosphorylate thymidine to TDP and TTP. In the nuclear fractions, the absolute activity of thymidine kinase increases from 16 to 46 h after hepatectomy but represents a decreasing proportion of the activity of the homogenate. At the same time, the proportion of kinase activity rises markedly in the supernatant fraction with a maximum of 83% in 40 h regenerating livers. The implications of these results are discussed.