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Ligand Concentration (ligand + concentration)
Selected AbstractsA Study of Heavy Metal Complexation in Grape JuiceELECTROANALYSIS, Issue 5-6 2005Íñigo Salinas Abstract Differential pulse anodic stripping voltammetry, DPASV, has been used to monitor the initial stages of grape juice fermentation, focusing on Zn interactions with natural occurring ligands. Langmuir and Scatchard linearization methods have been employed. A 1,:,1 ratio has been found by either method; from Langmuir data analysis only one ligand population was found, while Scatchard approach gave rise to the detection of two ligand types. Both data analysis procedures led to the same total ligand concentration. When catechin was used as model ligand, a 1,:,1 ratio was found for Zn and also for Cu. [source] Flow-through partial-filling affinity capillary electrophoresis can estimate binding constants of neutral ligands to receptors via a competitive assay techniqueELECTROPHORESIS, Issue 6 2003John Kaddis Abstract This work evaluates the use of a competitive binding assay using flow-through partial-filling affinity capillary electrophoresis (FTPFACE) to estimate binding constants of neutral ligands to a receptor. We demonstrate this technique using, as a model system, carbonic anhydrase B (CAB, EC 4.2.1.1) and arylsulfonamides. In this technique, the capillary is first partially filled with a negatively charged ligand, a sample containing CAB and two noninteracting standards, and a neutral ligand, then electrophoresed. Upon application of a voltage the sample plug migrates into the plug of negatively charged ligand (L,) resulting in the formation of a CAB-L, complex. Continued electrophoresis results in mixing between the neutral ligand (L0) and the CAB-L, complex. L0 successfully competes out L, to form the new CAB-L0 complex. Analysis of the change in the relative migration time ratio (RMTR) of CAB relative to the noninteracting standards, as a function of neutral ligand concentration, yields a value for the binding constant. These values are in agreement with those estimated using other binding and ACE techniques. Data demonstrating the quantitative potential of this method is presented. [source] 3-D Water-Soluble Reversible Neodymium(III) and Lanthanum(III) Coordination PolymersEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2004Tina Vermonden Abstract The formation of soluble supramolecular 3-D coordination polymers with Nd3+ and La3+ in aqueous solution has been studied for two bifunctional ligands consisting of two pyridine-2,6-dicarboxylate groups connected at the 4-position by O(CH2CH2O)4 and O(CH2CH2O)6 spacers (C4 and C6, respectively). Viscosity measurements were used to monitor the network formation as a function of the ligand concentration, and the ratio between metal ions and ligands. For corresponding conditions C4 solutions with Nd3+ always gave much higher viscosities than C6 solutions with Nd3+. C6 is long, and flexible enough to bind with both chelating groups to only one metal ion (ring formation). This causes the polymers to stop growing, resulting in smaller average sizes of the 3-D polymers. The ring-structures could be demonstrated by 1H NMR spectroscopy using C6 and La3+ at low concentrations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] The effect of ligand on the rate of propagation of Cu(0)-wire catalyzed SET-LRP of MA in DMSO at 25 °CJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2009Nga H. Nguyen Abstract The effect of initial ligand concentration on the apparent rate constant of propagation of single-electron transfer living radical polymerization (SET-LRP) of MA in DMSO at 25 °C was examined using various lengths of Cu(0) wire as catalyst. It was determined that unlike other parameters such as initiator concentration, solvent concentration, and deactivator concentration, no simple external rate-order for the ligand concentration could be determined. Rather, the response of the rate of SET-LRP to initial ligand concentration is complex and is likely determined by a competition of ligand-dependent extent of disproportionation as well as the role of ligand concentration in the surface mediated activation process. Results suggest that a minimum concentration of ligand is needed to achieve both acceptable reaction rate and reaction control, and therefore, ligand concentration must be considered in designing experimental conditions for SET-LRP. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5629,5638, 2009 [source] Reduction of the amyloidogenicity of a protein by specific binding of ligands to the native conformationPROTEIN SCIENCE, Issue 4 2001Fabrizio Chiti AcP, acylphosphatase; CD, circular dichroism; TFE, 2,2,2-trifluoroethanol; TTR, transthyretin Abstract It is known that human muscle acylphosphatase (AcP) is able, under appropriate conditions in vitro, to aggregate and form amyloid fibrils of the type associated with human diseases. A number of compounds were tested for their ability to bind specifically to the native conformation of AcP under conditions favoring denaturation and subsequent aggregation and fibril formation. Compounds displaying different binding affinities for AcP were selected and their ability to inhibit protein fibrillization in vitro was evaluated. We found that compounds displaying a relatively high affinity for AcP are able to significantly delay protein fibrillization, mimicking the effect of stabilizing mutations; in addition, the effectiveness of such outcome correlates positively to both ligand concentration and affinity to the native state of AcP. By contrast, the inhibitory effect of ligands on AcP aggregation disappears in a mutant protein in which such binding affinity is lost. These results indicate that the stabilization of the native conformation of amyloidogenic proteins by specific ligand binding can be a strategy of general interest to inhibit amyloid formation in vivo. [source] Analyzing ligand depletion in a saturation equilibrium binding experimentBIOCHEMISTRY AND MOLECULAR BIOLOGY EDUCATION, Issue 6 2006Enrique Claro Abstract I present a proposal for a laboratory practice to generate and analyze data from a saturation equilibrium binding experiment addressed to advanced undergraduate students. [3H]Quinuclidinyl benzilate is a nonselective muscarinic ligand with very high affinity and very low nonspecific binding to brain membranes, which contain a high density of muscarinic receptors. These features allow the instructor to devote especial emphasis to evaluate ligand depletion, and therefore, stress the subtle but fundamental difference between total (added) ligand and free ligand concentration at equilibrium. [source] Effects of Epidermal Growth Factor on Fibroblast Migration through Biomimetic HydrogelsBIOTECHNOLOGY PROGRESS, Issue 6 2003Andrea S. Gobin We have previously reported on the development and use of synthetic hydrogel extracellular matrix (ECM) analogues that can be used to study the mechanisms of migration. These biomimetic hydrogels consist of bioinert poly(ethylene glycol) diacrylate derivatives with proteolytically degradable peptide sequences included in the backbone of the polymer and adhesion peptide sequences grafted into the network. Cells adhere to the hydrogel via interaction between the grafted adhesion ligands and receptors on the cell surface. The cells migrate through the three-dimensional system by secreting the appropriate proteolytic enzymes, which are involved in cell migration and are targeted to the peptide sequences incorporated in the backbone of the polymer. It was observed that cell migration has a biphasic dependence on adhesion ligand concentration, with optimal migration at intermediate ligand levels. In this study, we demonstrate that we can covalently attach epidermal growth factor (EGF) to PEG and graft them into the hydrogels. It was observed that EGF when tethered maintained mitogenic activity. It was also observed that fibroblast migration significantly increased in the presence of the grafted EGF through the collagenase-sensitive hydrogels. In addition, the increase in migration was found to be independent from the proliferative response of the cells. These synthetic ECM analogues allow one to systematically control identities and concentrations of biomolecules and are useful tools to study mechanisms of cell migration. [source] Parsing the Effects of Binding, Signaling, and Trafficking on the Mitogenic Potencies of Granulocyte Colony-Stimulating Factor AnaloguesBIOTECHNOLOGY PROGRESS, Issue 3 2003Casim A. Sarkar The pharmacodynamic potency of a therapeutic cytokine interacting with a cell-surface receptor can be attributed primarily to three central properties: [1] cytokine/receptor binding affinity, [2] cytokine/receptor endocytic trafficking dynamics, and [3] cytokine/receptor signaling. Thus, engineering novel or second-generation cytokines requires an understanding of the contribution of each of these to the overall cell response. We describe here an efficient method toward this goal in demonstrated application to the clinically important cytokine granulocyte colony-stimulating factor (GCSF) with a chemical analogue and a number of genetic mutants. Using a combination of simple receptor-binding and dose-response proliferation assays we construct an appropriately scaled plot of relative mitogenic potency versus ligand concentration normalized by binding affinity. Analysis of binding and proliferation data in this manner conveniently indicates which of the cytokine properties,binding, trafficking, and/or signaling,are contributing substantially to altered potency effects. For the GCSF analogues studied here, two point mutations as well as a poly(ethylene glycol) chemical conjugate were found to have increased potencies despite comparable or slightly lower affinities, and trafficking was predicted to be the responsible mechanism. A third point mutant exhibiting comparable binding affinity but reduced potency was predicted to have largely unchanged trafficking properties. Surprisingly, another mutant possessing an order-of-magnitude weaker binding affinity displayed enhanced potency, and increased ligand half-life was predicted to be responsible for this net beneficial effect. Each of these predictions was successfully demonstrated by subsequent measurements of depletion of these five analogues from cell culture medium. Thus, for the GCSF system we find that ligand trafficking dynamics can play a major role in regulating mitogenic potency. Our results demonstrate that cytokine analogues can exhibit pharmacodynamic behaviors across a diverse spectrum of "binding-potency space" and that our analysis through normalization can efficiently elucidate hypotheses for the underlying mechanisms for further dedicated testing. We have also extended the Black-Leff model of pharmacological agonism to include trafficking effects along with binding and signaling, and this model provides a framework for parsing the effects of these factors on pharmacodynamic potency. [source] Vesicles to Concentrate Iron in Low-Iron Media: An Attempt to Mimic Marine SiderophoresCHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2008Lucie Bednarova Dr. Abstract Amphiphilic catechol-type iron chelators were studied with the aim of mimicking the properties of marine bacterial siderophores. The FeIII complexation constants and aqueous solution speciation of LS10, a sulfonated catechol unit that has a C10 lipophilic carbon chain connected by an amide linkage, were determined by spectrophotometric titration. The calculated value of pFe3+ is 18.1 at pH,7.4. Cryogenic transmission electron microscopy showed that the tris(catecholate) ferric complex formed at physiological pH initially assembles into micelles, in which the catecholate,iron units stay on the exterior of the micelle. The average diameter of these micelles was estimated to be 4.2,nm. The micelles then slowly rearrange into clusters of different sizes, which leads to the formation of unilamellar and bilamellar vesicles. The reorganization processes are comparable to those observed by Butler et al. for the marinobactin siderophores produced by marine bacteria, but in contrast to the marinobactins, vesicles of the Fe3+,LS10 complex form without an excess of iron relative to ligand concentration. The time-dependent micelle-to-vesicle transition is discussed herein. [source] Facilitated Transfer of Alkali Metal Ions by a Tetraester Derivative of Thiacalix[4]arene at the Liquid,Liquid InterfaceELECTROANALYSIS, Issue 12 2008Akgemci, Emine Guler Abstract The facilitated transfer of alkali metal ions (Na+, K+, Rb+, and Cs+) by 25,26,27,28-tetraethoxycarbonylmethoxy-thiacalix[4]arene across the water/1,2-dichloroethane interface was investigated by cyclic voltammetry. The dependence of the half-wave transfer potential on the metal and ligand concentrations was used to formulate the stoichiometric ratio and to evaluate the association constants of the complexes formed between ionophore and metal ions. While the facilitated transfer of Li+ ion was not observed across the water/1,2-dichloroethane interface, the facilitated transfers were observed by formation of 1,:,1 (metal:ionophore) complex for Na+, K+, and Rb+ ions except for Cs+ ion. In the case of Cs+ a 1,:,2 (metal:ionophore) complex was obtained from its special electrochemical response to the variation of ligand concentrations in the organic phase. The logarithms of the complex association constants, for facilitated transfer of Na+, K+, Rb+, and Cs+, were estimated as 6.52, 7.75, 7.91 (log ,1°), and 8.36 (log ,2°), respectively. [source] Formation of copper complexes in landfill leachate and their toxicity to zebrafish embryosENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2000Jonathon K. Fraser Abstract Toxic metal organic complexeshavenot been found in natural waters, although someorganicacids form bioavailable lipophilic and metabolite-type metal complexes. Landfill leachates usually contain organic acids and in the urban environment these leachates, when mixed with storm waters containing Cu, could be a source of toxic Cu organic complexes in streams and estuaries. We investigated the formation of Cu complexes in the leachate from an active urban landfill and found that some of the complexes formed were toxic to zebrafish embryos. High and low nominal molecular weight (NMWT) fractions; >5,000 Da and <700 Da, of leachate both formed Cu complexes with almost identical Cu complexing characteristics but the toxicity was due solely to the low NMWT complexes formed in the <700 Da fraction. Chemical equilibrium modelling with MINTEQA2 and H and Cu complex conditional association constants and ligand concentrations obtained from pH and Cu titrations with a Cu ion-selective electrode and van den Berg,Ruzic analyses of the titration data was used to calculate the copper speciation in the embryo test solutions. This calculated speciation, which was confirmed by measurements of Cu2+ in the test solutions, enabled the toxicity due to the free Cu ion and to the Cu complexes to be distinguished. [source] Bortezomib reduces serum dickkopf-1 and receptor activator of nuclear factor- ,B ligand concentrations and normalises indices of bone remodelling in patients with relapsed multiple myelomaBRITISH JOURNAL OF HAEMATOLOGY, Issue 5 2006Evangelos Terpos Summary The effect of bortezomib on bone remodelling was evaluated in 34 relapsed myeloma patients. At baseline, patients had increased serum concentrations of dickkopf-1 (DKK-1), soluble receptor activator of nuclear factor- ,B ligand (sRANKL), sRANKL/osteoprotegerin ratio, C-telopeptide of type-I collagen (CTX) and tartrate-resistant acid phosphatase isoform-5b (TRACP-5b); bone-alkaline phosphatase and osteocalcin were reduced. Serum DKK-1 correlated with CTX and severe bone disease. Bortezomib administration significantly reduced serum DKK-1, sRANKL, CTX, and TRACP-5b after four cycles, and dramatically increased bone-alkaline phosphatase and osteocalcin, irrespective of treatment response. This is the first study showing that bortezomib reduces DKK-1 and RANKL serum levels, leading to the normalisation of bone remodelling in relapsed myeloma. [source] | |||||||||||||