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Different Monovalent Cations (different + monovalent_cation)
Selected AbstractsCharacterization of Arginine Transport in Helicobacter pyloriHELICOBACTER, Issue 4 2003George L. Mendz ABSTRACT Background. The amino acid L-arginine is an essential requirement for growth of Helicobacter pylori. Several physiological roles of this amino acid have been identified in the bacterium, but very little is known about the transport of L-arginine and of other amino acids into H. pylori. Methods. Radioactive tracer techniques using L-(U- 14C) arginine and the centrifugation through oil method were employed to measure the kinetic parameters, temperature dependence, substrate specificity, and effects of analogues and inhibitors on L-arginine transport. Results. The transport of arginine at millimolar concentrations was saturable with a Km of 2.4 ± 0.3 mM and Vmax of 1.3 ± 0.2 pmole min,1 (µl cell water),1 or 31 ± 3 nmole per minute (mg protein),1 at 20°C, depended on temperature between 4 and 40°C, and was susceptible to inhibitors. These characteristics suggested the presence of one or more arginine carriers. The substrate specificity of the transport system was studied by measuring the effects of L-arginine analogues and amino acids on the rates of transport of L-arginine. The absence of inhibition in competition experiments with L-lysine and L-ornithine indicated that the transport system was not of the Lysine-Arginine-Ornithine or Arginine-Ornithine types. The presence of different monovalent cations did not affect the transport rates. Several properties of L-arginine transport were elucidated by investigating the effects of potential inhibitors. Conclusions. The results provided evidence that the transport of L-arginine into H. pylori cells was carrier-mediated transport with the driving force supplied by the chemical gradient of the amino acid. [source] Environmentally responsive micelles from polystyrene,poly[bis(potassium carboxylatophenoxy)phosphazene] block copolymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2005Youngkyu Chang Abstract Amphiphilic diblock copolymers that contained hydrophilic poly[bis(potassium carboxylatophenoxy)phosphazene] segments and hydrophobic polystyrene sections were synthesized via the controlled cationic polymerization of Cl3PNSiMe3 with a polystyrenyl,phosphoranimine as a macromolecular terminator. These block copolymers self-associated in aqueous media to form micellar structures which were investigated by fluorescence spectroscopy, dynamic light scattering, and transmission electron microscopy. The size and shape of the micelles were not affected by the introduction of different monovalent cations (Li+, K+, Na+, and Cs+) into the stable micellar solutions. However, exposure to divalent cations induced intermicellar crosslinking through carboxylate groups, which caused precipitation of the ionically crosslinked aggregates from solution. This micelle-coupling behavior was reversible: the subsequent addition of monovalent cations caused the redispersion of the polystyrene- block -poly[bis(potassium carboxylatophenoxy)phosphazene] (PS,KPCPP) block copolymers into a stable micellar solution. Aqueous micellar solutions of PS,KPCPP copolymers also showed pH-dependent behavior. These attributes make PS,KPCPP block copolymers suitable for studies of guest retention and release in response to ion charge and pH. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2912,2920, 2005 [source] Monovalent cations affect the free solution mobility of DNA by perturbing the hydrogen-bonded structure of water,BIOPOLYMERS, Issue 2 2005Earle Stellwagen Abstract The free solution mobilities of single- and double-stranded DNA molecules of various molecular weights have been measured by capillary electrophoresis in solutions of constant ionic strength containing a common anion and fifteen different monovalent cations. In solutions with the same ionic composition, the mobilities of different DNA molecules can vary by up to 20%, depending on molecular weight, the number of strands, and the presence or absence of A-tracts, runs of four or more contiguous adenine residues. Importantly, the mobilities observed for the same DNA sample can vary by up to 40% in solutions containing different cations. The mobility differences observed for the same DNA in solutions containing different cations cannot be rationalized by differences in the anhydrous radii or intrinsic conductivities of the various cations, or by the sequence-dependent binding of certain cations to A-tracts. Instead, the observed mobilities are linearly correlated with the average number of water,water hydrogen bonds that are present in solutions containing different cations. The mobilities are also correlated with the viscosity B coefficients of the various cations and with the rotational correlation times frictional coefficients observed for water molecules in solutions containing different cations. Hence, monovalent cations modify the free solution mobility of DNA primarily by perturbing the hydrogen-bonded structure of water, affecting the friction experienced by the migrating DNA molecules during electrophoresis. © 2005 Wiley Periodicals, Inc. Biopolymers 78: 62,68, 2005 [source] Self-Assembled Ionophores from Isoguanosine: Diffusion NMR Spectroscopy Clarifies Cation's and Anion's Influence on Supramolecular StructureCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2007Tamar Evan-Salem Abstract Cation-templated self-assembly of the lipophilic isoguanosine (isoG,1) with different monovalent cations (M+=Li+, Na+, K+, NH4+, and Cs+) was studied in solvents of different polarity by using diffusion NMR spectroscopy. Previous studies that did not use diffusion NMR techniques concluded that isoG,1 forms both pentamers (isoG,1)5,M+ and decamers (isoG,1)10,M+ in the presence of alkali-metal cations. The present diffusion NMR studies demonstrate, however, that isoG,1 does not form (isoG,1)5,M+ pentamers. In fact, the diffusion NMR data indicates that both doubly charged decamers of formula (isoG,1)10,2,M+ and singly charged decamers, (isoG,1)10,M+, are formed with lithium, sodium, potassium, and ammonium tetraphenylborate salts (LiB(Ph)4, KB(Ph)4, NaB(Ph)4 and NH4B(Ph)4), depending on the isoG,1:salt stoichiometry of the solution. In the presence of CsB(Ph)4, isoG,1 affords only the singly charged decamers (isoG,1)10,Cs+. By monitoring the diffusion coefficient of the B(Ph)4, ion in the different mixtures of solvents, we also concluded that the anion is more strongly associated to the doubly charged decamers (isoG,1)10,2,M+ than to the singly charged decamers (isoG,1)10,M+. The (isoG,1)10,2,M+ species can, however, exist in solution without the mediation of the anion. This last conclusion was supported by the finding that the doubly charged decamers (isoG,1)10,2,M+ also prevail in 1:1 CD3CN:CDCl3, a solvent mixture in which the B(Ph)4, ion does not interact significantly with the self-assembled complex. These diffusion measurements, which have provided new and improved structural information about these decameric isoG,1 assemblies, demonstrate the utility of combining diffusion NMR techniques with conventional NMR methods in seeking to characterize labile, multicomponent, supramolecular systems in solution, especially those with high symmetry. [source] | ||||||||||