Publications

• Ligand-induced dimer-to-tetramer transformation in cytosine triphosphate synthetase.

  Levitzki A., Koshland D.E. Jr.

  Biochemistry 11:247-253(1972) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Cloning and verification of the Lactococcus lactis pyrG gene and characterization of the gene product, CTP synthase.

  Wadskov-Hansen S.L.L., Willemoes M., Martinussen J., Hammer K., Neuhard J., Larsen S.

  The pyrG gene of Lactococcus lactis subsp. cremoris, encoding CTP synthase, has been cloned and sequenced. It is flanked upstream by an open reading frame showing homology to several aminotransferases and downstream by an open reading frame of unknown function. L. lactis strains harboring disrupte ... >> More

  The pyrG gene of Lactococcus lactis subsp. cremoris, encoding CTP synthase, has been cloned and sequenced. It is flanked upstream by an open reading frame showing homology to several aminotransferases and downstream by an open reading frame of unknown function. L. lactis strains harboring disrupted pyrG alleles were constructed. These mutants required cytidine for growth, proving that in L. lactis, the pyrG product is the only enzyme responsible for the amination of UTP to CTP. In contrast to the situation in Escherichia coli, an L. lactis pyrG mutant could be constructed in the presence of a functional cdd gene encoding cytidine deaminase. A characterization of the enzyme revealed similar properties as found for CTP synthases from other organisms. However, unlike the majority of CTP synthases the lactococcal enzyme can convert dUTP to dCTP, although a half saturation concentration of 0.6 mm for dUTP makes it unlikely that this reaction plays a significant physiological role. As for other CTP synthases, the oligomeric structure of the lactococcal enzyme was found to be a tetramer, but unlike most of the other previously characterized enzymes, the tetramer was very stable even at dilute enzyme concentrations. << Less

  J. Biol. Chem. 276:38002-38009(2001) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Mechanistic investigations of Escherichia coli cytidine-5'-triphosphate synthetase. Detection of an intermediate by positional isotope exchange experiments.

  von der Saal W., Anderson P.M., Villafranca J.J.

  CTP synthetase from Escherichia coli catalyzes exchange of 18O from the beta gamma-bridge position of [gamma-18O4] ATP into the beta-nonbridge position. This positional isotope exchange occurs in the presence of UTP and MgCl2 but in the absence of NH3. The enzyme also has an ATPase activity in the ... >> More

  CTP synthetase from Escherichia coli catalyzes exchange of 18O from the beta gamma-bridge position of [gamma-18O4] ATP into the beta-nonbridge position. This positional isotope exchange occurs in the presence of UTP and MgCl2 but in the absence of NH3. The enzyme also has an ATPase activity in the presence of UTP that occurs under conditions that are identical to those used in the positional isotope exchange experiments. These data provide evidence for the stepwise nature of the reactions catalyzed by CTP synthetase with the initial step involving phosphorylation of UTP by ATP. The relative rate of the isotope exchange reaction is approximately 3 times faster than the ATPase reaction, but the isotope exchange rate is approximately 3% of the overall rate in the presence of NH3. These results are consistent with the ATPase reaction involving attack of water on the phosphorylated intermediate (4-phospho-UTP). The positional isotope exchange reaction is independent of the UTP concentration above saturating levels of UTP demonstrating that the order of addition of substrates is UTP followed by ATP and then NH3. << Less

  J Biol Chem 260:14993-14997(1985) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Investigation of the mechanism of CTP synthetase using rapid quench and isotope partitioning methods.

  Lewis D.A., Villafranca J.J.

  The UTP-dependent ATPase reaction and the glutamine-dependent overall reaction of Escherichia coli CTP synthetase have been studied by rapid quench and isotope partitioning kinetics. The effect of GTP, an allosteric effector, on the pre-steady-state kinetics of both reactions has also been examine ... >> More

  The UTP-dependent ATPase reaction and the glutamine-dependent overall reaction of Escherichia coli CTP synthetase have been studied by rapid quench and isotope partitioning kinetics. The effect of GTP, an allosteric effector, on the pre-steady-state kinetics of both reactions has also been examined. The time courses of the UTP-dependent ATPase reaction in the presence and absence of GTP are both characterized by a burst of acid-labile phosphate equivalent to 0.93 and 0.43 subunits, respectively. The time course of the glutamine-dependent reaction in the absence of GTP is also characterized by a burst of acid-labile phosphate corresponding to 0.8 subunit; however, in the presence of GTP, no burst was observed. These results along with positional isotope exchange experiments [von der Saal, W., Anderson, P. M., & Villafranca, J. J. (1985) J. Biol. Chem. 260, 14997] provide evidence that the mechanism of CTP formation involves phosphorylation of UTP followed by attack of NH3, and finally release of phosphate, producing CTP, ADP, and Pi. A kinetic model for the first stages of the enzymatic reaction was developed from the rapid quench data, and the internal equilibrium constant for the formation of the phosphorylated UTP intermediate was determined. The internal equilibrium constants for the UTP-dependent reaction in the presence and absence of GTP were found to be 1.1 and 18, respectively. By contrast, the internal equilibrium constant for the reaction in the presence of glutamine was 50. Thus, the presence of glutamine shifts the internal equilibrium constant to favor formation of the phosphorylated UTP intermediate.(ABSTRACT TRUNCATED AT 250 WORDS) << Less

  Biochemistry 28:8454-8459(1989) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Enzymatic amination of uridine triphosphate to cytidine triphosphate.

  LIEBERMAN I.

  J Biol Chem 222:765-775(1956) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.