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Dissociation Kinetics (dissociation + kinetics)

Distribution by Scientific Domains
Chemistry75%

Selected Abstracts

Application of a Carbon Paste Electrode Modified with a Schiff Base Ligand to Mercury Speciation in Water

ELECTROANALYSIS, Issue 11 2005
Montserrat Colilla
Abstract A carbon paste electrode, modified with benzylbisthiosemicarbazone is used for mercury speciation in water samples. Mercury ion is selectively accumulated on the electrode surface at open circuit and its analysis was performed by cyclic voltammetry or square-wave voltammetry (SWV). A detection limit of 8,,g L,1 (3,) was found for 15,min of accumulation using SWV as measurement technique. The effect of several metallic ions and organic substances on voltammetric signal is examined. For speciation purposes, a ligand competition methodology between ligands in solution and electrode is used. Model mercury complexes are characterized as a function of their dissociation kinetics. The method was applied to mercury speciation in water samples from the Jarama River in Madrid. [source]

Measurement of dissociation rate of biomolecular complexes using CE

ELECTROPHORESIS, Issue 3 2009
Peilin Yang
Abstract Fluorescence anisotropy (FA), non-equilibrium CE of equilibrium mixtures (NECEEM) and high-speed CE were evaluated for measuring dissociation kinetics of peptide,protein binding systems. Fyn-SH3-SH2, a protein construct consisting of the src homology 2 (SH2) and 3 (SH3) domain of the protein Fyn, and a fluorescein-labeled phosphopeptide were used as a model system. All three methods gave comparable half-life of,53,s for Fyn-SH3-SH2:peptide complex. Achieving satisfactory results by NECEEM required columns over 30,cm long. When using Fyn-SH2-SH3 tagged with glutathione S -transferase (GST) as the binding protein, both FA and NECEEM assays gave evidence of two complexes forming with the peptide, yet neither method allowed accurate measurement of dissociation rates for both complexes because of a lack of resolution. High-speed CE, with a 7,s separation time, enabled separation of both complexes and allowed determination of dissociation rate of both complexes independently. The two complexes had half-lives of 22.0±2.7 and 58.8±6.1,s, respectively. Concentration studies revealed that the GST-Fyn-SH3-SH2 protein formed a dimer so that complexes had binding ratios of 2:1 (protein-to-peptide ratio) and 2:2. Our results demonstrate that although all methods are suitable for 1:1 binding systems, high-speed CE is unique in allowing multiple complexes to be resolved simultaneously. This property allows determination of binding kinetics of complicated systems and makes the technique useful for discovering novel affinity interactions. [source]

Presence of membrane ecdysone receptor in the anterior silk gland of the silkworm Bombyx mori

FEBS JOURNAL, Issue 15 2004
Mohamed Elmogy
Nongenomic action of an insect steroid hormone, 20-hydroxyecdysone (20E), has been implicated in several 20E-dependent events including the programmed cell death of Bombyx anterior silk glands (ASGs), but no information is available for the mode of the action. We provide evidence for a putative membrane receptor located in the plasma membrane of the ASGs. Membrane fractions prepared from the ASGs exhibit high binding activity to [3H]ponasterone A (PonA). The membrane fractions did not contain conventional ecdysone receptor as revealed by Western blot analysis using antibody raised against Bombyx ecdysone receptor A (EcR-A). The binding activity was not solubilized with 1,m NaCl or 0.05% (w/v) MEGA-8, indicating that the binding sites were localized in the membrane. Differential solubilization and temperature-induced phase separation in Triton X-114 showed that the binding sites might be integrated membrane proteins. These results indicated that the binding sites are located in plasma membrane proteins, which we putatively referred to as membrane ecdysone receptor (mEcR). The mEcR exhibited saturable binding for [3H]PonA (Kd = 17.3 nm, Bmax = 0.82 pmol·mg,1 protein). Association and dissociation kinetics revealed that [3H]PonA associated with and dissociated from mEcR within minutes. The combined results support the existence of a plasmalemmal ecdysteroid receptor, which may act in concert with the conventional EcR in various 20E-dependent developmental events. [source]

Entropy considerations in kinetic method experiments

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 9 2004
Chrys WesdemiotisArticle first published online: 7 SEP 200
Abstract In extended kinetic method experiments, relative binding enthalpies (,affinities') and relative entropies are obtained based on unimolecular dissociation kinetics. A series of ion-bound dimers AXBi is formed, in which the sample (A) and structurally similar reference molecules (Bi) are bridged by a central cation or anion (X). The branching ratios of the AXBi set to AX and BiX are determined at different internal energies, usually by subjecting AXBi to collisionally activated dissociation at various collision energies. The dependence of the natural logarithm of the branching ratios on the corresponding BiX bond enthalpies (X affinities of Bi) is evaluated as a function of internal energy to thereby deduce the AX bond enthalpy (X affinity of A) as well as an apparent relative entropy of the competitive dissociation channels, ,(,Sapp). Experiments with proton- and Na+ -bound dimers show that this approach can yield accurate binding enthalpies. In contrast, the derived ,(,Sapp) values do not correlate with the corresponding thermodynamic entropy differences between the channels leading to AX and BiX, even after scaling. The observed trends are reconciled by the transition state switching model. According to this model, the kinetics of barrierless dissociations, such as those encountered in kinetic method studies, are dominated by a family of tight transition states (,entropy bottlenecks') lying lower in energy than the corresponding dissociation thresholds. In general, the relative energies of these tight transition states approximately match those of the dissociation products, but their relative entropies tend to be much smaller, as observed experimentally. Copyright © 2004 John Wiley & Sons, Ltd. [source]