Differences between pyrimidine nucleoside monophosphate kinase from rat Novikoff ascites hepatoma and rat liver

Pyrimidine nucleoside monophosphate kinase [deoxycytidine monophosphate:adenosine triphosphate (dCMP:ATP) phosphotransferase. EC 2.7.4.14] has been purified from rat Novikoff ascites hepatoma and rat liver, each to a single major band appearing on sodium dodecyl sulfate polyacrylamide gel electrophoresis. Differences exist in regard to efficiency and regulation of enzymatic activities. The Km values of the tumor kinase for cytidine monophosphate (CMP) (0.0053 +/- 0.0008 MM) and dCMP (0.715 +/- 0.068 MM) are approximately one-fourth the Km values of the rat liver kinase, for CMP (0.030 +/- 0.007 MM) and dCMP (2.77 +/- 0.39 MM). The tumor dCMP kinase exhibits a lower Km for ATP (0.134 +/- 0.008 MM) than the rat liver kinase (0.68 +/- 0.09 mM). Moreover, the dCMP:CMP kinase activity ratio for the tumor enzyme is 1.12, while that for the rat liver enzyme is 0.45. The uridine monophosphate:CMP kinase activity ratio for the tumor enzyme is 1.93, while that for the rat liver enzyme is 2.68. Lower concentrations of dithiothreitol are required for 50% reactivation of the tumor dCMP kinase (1.00 mM) and CMP kinase (0.10 mM) than rat liver dCMP kinase (2.20 mM) and CMP kinase (0.57 mM). Thus, the kinase from Novikoff hepatoma exhibits properties of increased efficiency and relaxed regulation of activity which render it more suitable for a tumor, in which active DNA synthesis is ongoing.