A pyrimidine nucleoside monophosphate kinase from rat liver

A pyrimidine nucleoside monophosphate kinase has been purified 2100-fold from rat liver. With ATP and dATP as phosphate donors the kinase uses CMP, dCMP, and UMP as phosphate acceptors. Ara-CMP is also phosphorylated by the kinase. In contrast to dCMP and UMP, CMP can be phosphorylated by dCTP. CTP and ara-CTP cannot substitute for dCTP. The stringent specificity of the phosphate donor site for ATP and dATP is lost when CMP serves as acceptor. All nucleoside triphosphates act as donors to a significant extent. No evidence has been found to suggest more than one enzyme. All activities, to different degrees, are strictly dependent upon preincubation at 37 degrees with a sulfhydryl reducing agent. Various reagents (85 mM) are ranked in order of increasing effectiveness of reactivation as follows: dithiothretiol greater than glutathione larger than or equal to 2-mercaptoethanol greater than L-cysteine greater than DL-alpha-lipoic acid. A NADP+-dependent thioredoxin (17 muM)-thioredoxin reductase system from Novikoff ascites rat tumor was found to be the most powerful reducing agent tested. CTP, dCTP, UTP, and dTTP (1 mM) do not affect the kinase activity regardless of the phosphate acceptor.