FRACTIONATION OF THYMIDINE PHOSPHOKINASE, THYMIDINE 5'-MONOPHOSPHATE PHOSPHOKINASE AND THYMIDINE 5'-DIPHOSPHATE PHOSPHOKINASE IN EXTRACTS OF LANDSCHUTZ ASCITES-TUMOUR CELLS.

1. Extracts of Landschutz ascites-tumour cells have been fractionated by treatment with acid, alumina C(gamma) gel and Sephadex G-100 to yield purified preparations of thymidine phosphokinase, thymidine 5'-monophosphate phosphokinase and thymidine 5'-diphosphate phosphokinase. 2. These results clearly demonstrate the existence in Landschutz ascites tumour of three phosphokinases each of which catalyses one step in the reaction sequence: thymidineright harpoon over left harpoonthymidine 5'-monophosphateright harpoon over left harpoonthymidine 5'-diphosphateright harpoon over left harpoonthymidine 5'-triphosphate. Though these results do not preclude the participation of other enzymes in the formation of thymidine 5'-triphosphate from thymidine by Landschutz ascites-tumour cells, they provide strong support for the view that thymidine 5'-diphosphate is an intermediate in the formation of thymidine 5'-triphosphate from thymidine 5'-monophosphate by this system.