Pyrimidine nucleoside monophosphate kinase from human leukemic blast cells.

Pyrimidine nucleoside monophosphate kinase (EC 2.7.4.14) catalyzes the phosphorylation of various pyrimidine nucleoside monophosphates to their corresponding diphosphates. In addition to its role in the synthesis of nucleic acid precursors, this enzyme is essential for the conversion of the antileukemic agent 1-/3-o-arabinofuranosylcytosine to its active metabolite 1-/3-o-arabinofuranosyl 5 -triphosphate. Pyrimidine nucleoside monophosphate kinase has been purified 520-fold from human leukemic blast cells. Substrate specificity and kinetics for various pyrimidine nucleoside monophosphates and ana logs have been investigated and compared with previous studies of this kinase isolated from other sources. A single enzyme appears responsible for the phosphoryla tion of cytidine 5 -monophosphate, deoxycytidine 5 monophosphate, uridine 5 -monophosphate, and deoxyuridine 5 -monophosphate as well as the pharmacological substrates 1-0-D-arabinofuranosylcytosine 5 -monophosphate, 5-fluorouridine 5 -monophosphate, 5-fluorodeoxyuridine 5 -monophosphate, and 1-ß-o-arabinofuranosyluracil 5 -monophosphate. Enzyme levels of pyrimidine nucleoside monophosphate kinase have been deter mined in leukocyte blast cells isolated from normal human donors (1.16 units/mg protein) and from patients with acute lymphocytic leukemia (1.96 units/mg protein), acute myelogenous leukemia (1.99 units/mg protein), and chronic myelogenous leukemia (1.88 units/mg protein). These levels are 100-fold higher than those of deoxy cytidine kinase, the enzyme responsible for the initial phosphorylation of 1-ß-oarabmofuranosylcytosine. How ever, the affinity of deoxycytidine kinase for 1-/l-o-arabinofuranosylcytosine (K,„, 2.56 x 10 M) is greater than that of the monophosphate kinase for 1-/i-o-arabinofuranosylcytosine 5 -monophosphate (Kni, 6.8 x 10"* M).