Properties of deoxythymidine kinase partially purified from animal tumors.

The activity of deoxythymidine kinase appears related to the proliferative ability of the cell (l-6). In adult rat liver, deoxythymidine kinase activity is virtually undetectable but appears rapidly during liver regeneration (I, 5, 7-10); the enhancement in the latter case is completely blocked by X-irradiation (II). Deoxythymidine kinase activity is also markedly enhanced in the livers of rats sustained on a high protein diet (12) and in animal cells infected with virus in tissue culture (13-17). In addition, a correlation exists between the enzymatic synthesis or activity and the mitotic activity of certain plants. The activity markedly increased after the germination of wheat or corn seedlings (18). In the mitotic cycle of the lily microspores, deoxythymidine kinase appears during a precisely defined period and persists for only 24 hours (19). Not only is deoxythymidine kinase subject to induction and repression, but enzymatic activity is also inhibited by the distal product, deoxythymidine triphosphate, as reported by Maley and Maley in the chick embryo (20) ; Ives, Morse, and Potter (21); Bukovsky and Roth (22) in hepatomas; Breitman (23) in regenerating liver; Okazaki and Kornberg (24) in Escherichia coli; and this laboratory in hepatomas (6) and in human leukocytes (25). The involvement of deoxythymidine kinase in these regulatory mechanisms certainly suggest.s a more important role for this enzyme in the control of deoxyribonucleic acid metabolism. The studies present.ed herein were designed to investigate more fully the properties of deoxythymidine kinase isolated from tumors of mammalian origin and perhaps, in this manner, supply a molecular basis for the understanding of any regulatory mechanism.