Studies on the biosynthesis of deoxyribonucleic acid by extracts of mammalian cells IV. The phosphorylation of thymidine

Kinases responsible for the formation of thymine-deoxyribose-5′-monophosphate, diphosphate and triphosphate from thymine-deoxyribose have been purified from extracts of Ehrlich ascites carcinoma. These enzymes are also found in rabbit tissues, highest levels of activity being observed in thymus and bone marrow. In rat liver regenerating after partial hepatectomy thymine-deoxyribose, thymine-deoxyribose-5′-monophosphate and diphosphate kinases appear in that order, maximum activities being observed between 30 and 48 h after the operation. In cultures of L. strain fibroblasts there is again a sequential appearance of thymine-deoxyribose, thymine-deoxyribose-5′-monophosphate and diphosphate kinases during the early part of the growth phase and the activities of all three enzymes decline before the completion of growth. Growth of L. strain fibroblasts in a medium containing thymine-deoxyribose lead to increases in kinase activities which were compatible with enzyme induction.