Mammalian Deoxynucleoside Kinases

Abstract Deoxycytidine kinase, which catalyzes the phosphorylation of deoxycytidine (dCR) to form deoxycytidine monophosphate in the presence of specific nucleoside 5'-triphosphates and a cation, has been purified about 100-fold from extracts of calf thymus. This enzyme appeared also to catalyze the phosphorylation of an analogue of dCR, 1-β-d-arabinofuranosylcytosine (ara-C). The Km (4.0 x 10-5 m) for ara-C was found to be higher than the Km (1.4 x 10-5 m) for the natural substrate dCR. Both nucleosides could accept a phosphate group from the same phosphate donors; however, in each case, ara-C was much less active as a phosphate acceptor than dCR. dCMP, dCDP, and dCTP were all active as inhibitors of dCR kinase. Ara-C was more sensitive to the inhibition produced by these cytosine deoxynucleotides than dCR. The inhibition produced by dCTP appeared to be competitive with the phosphate donor (ATP) and noncompetitive with the phosphate acceptor (dCR or ara-C). In studies on the phosphorylation of dCR or ara-C, ara-C was found to be a competitive inhibitor of dCR (Ki, 3.6 x 10-5 m), and dCR was found to be a very potent competitive inhibitor of ara-C (Ki, 1.3 x 10-9 m).