Title : Phosphorylation of Cytidine - , Deoxycytidine - , and Their Analog - Monophosphates by Human UMP / CMP Kinase Is Differentially Regulated by ATP and Magnesium

Human UMP/CMP kinase (EC 2.7.4.14) is responsible for phosphorylation of CMP, UMP, and dCMP and also plays an important role in the activation of pyrimidine analogs, some of which are clinically useful anticancer or antiviral drugs. Previous kinetic data using recombinant or highly purified human UMP/CMP kinase showed that dCMP, as well as pyrimidine analog monophosphates, were much poorer substrates than CMP or UMP for this enzyme. This implies that other unidentified mechanisms must be involved to make phosphorylation of dCMP or pyrimidine analog monophosphates inside cells by this enzyme possible. Here, we re-evaluated the optimal reaction conditions for human recombinant human UMP/CMP kinase to phosphorylate dCMP and CMP (referred as dCMPK and CMPK activities). We found that ATP and magnesium (Mg) were important regulators of the kinase activities of this enzyme. Free Mg enhanced dCMPK activity but inhibited CMPK activity. Free ATP or excess ATP/Mg, on the other hand, inhibited dCMPK but not CMPK reactions. The differential regulation of dCMPK versus CMPK activities by ATP or Mg was also seen in other 2’-deoxy-pyrimidine analog monophosphates (dUMP, 5FdUMP, ara-C monophosphate, gemcitabine monophosphate) versus their This article has not been copyedited and formatted. The final version may differ from this version. Molecular Pharmacology Fast Forward. Published on November 18, 2004 as DOI: 10.1124/mol.104.006098 at A PE T Jornals on Jne 2, 2017 m oharm .aspeurnals.org D ow nladed from