potassium-thiocyanate and potassium-bromide

Thermophoresis or thermodiffusion has become an important tool to monitor protein-ligand binding as it is very sensitive to the nature of solute-water interactions. However, the microscopic mechanisms underlying thermodiffusion in protein systems are poorly understood at this time. One reason is the difficulty to separate the effects of the protein system of interest from the effects of buffers that are added to stabilize the proteins. Due to the buffers, typical protein solutions form multicomponent mixtures with several kinds of salt. To achieve a more fundamental understanding of thermodiffusion of proteins, it is therefore necessary to investigate solutions of buffer salts. For this work, the thermodiffusion of aqueous potassium salt solutions has been studied systematically. We use thermal diffusion forced Rayleigh scattering experiments in a temperature range from 15 °C to 45 °C to investigate the thermodiffusive properties of aqueous solutions of five potassium salts: potassium chloride, potassium bromide, potassium thiocyanate, potassium acetate, and potassium carbonate in a molality range between 1 mol/kg and 5 mol/kg. We compare the thermophoretic results with those obtained for non-ionic solutes and discuss the thermophoresis of the salts in the context of ion-specific solvation according to the Hofmeister series.

Topics: Bromides; Carbonates; Potassium; Potassium Acetate; Potassium Chloride; Potassium Compounds; Proteins; Solutions; Temperature; Thermal Diffusion; Thiocyanates; Water

It was established that nitrite in the presence of chloride, bromide, and thiocyanate decreases the rate of hydrogen peroxide decomposition by catalase. The decrease was recorded by the permanganatometric method and by a method of dynamic calorimetry. Nitrite was not destroyed in the course of the reaction and the total value of heat produced in the process was not changed by its presence. These facts suggest that nitrite induces inhibition of catalase with no change in the essence of the enzymatic process. Even micromolar nitrite concentrations induced a considerable decrease in catalase activity. However, in the absence of chloride, bromide, and thiocyanate inhibition was not observed. In contrast, fluoride protected catalase from nitrite inhibition in the presence of the above-mentioned halides and pseudohalide. As hydrogen peroxide is a necessary factor for triggering a number of important toxic effects of nitrite, the latter increases its toxicity by inhibiting catalase. This was shown by the example of nitrite-induced hemoglobin oxidation. The naturally existing gradient of chloride and other anion concentrations between intra- and extracellular media appears to be the most important mechanism of cell protection from inhibition of intracellular catalase by nitrite. Possible mechanisms of this inhibition are discussed.

Topics: Animals; Bromides; Catalase; Cattle; Enzyme Inhibitors; Fluorides; Hemoglobins; Hydrogen Peroxide; Hydrogen-Ion Concentration; Kinetics; Liver; Nitrites; Oxidation-Reduction; Potassium Compounds; Sodium Chloride; Thermodynamics; Thiocyanates

Effect of gamma radiation on flavocytochrome b2 in dilute aqueous solution was studied. A study of the effect of the radiolytically produced inorganic free-radical anions such as I2.-, Br2.- and (SCN)2.- on the enzyme activity indicates the involvement of cysteine and tyrosine residues in the catalytic activity of flavocytochrome b2. The changes in kinetic parameters, i.e., Michaelis-Menten constant Km and maximal velocity Vmax, due to irradiation under different conditions suggest that radiation induced enzyme inactivation is the result of destruction of active-site residues as well as modification of the substrate binding site. Fluorescence studies of unirradiated and irradiated enzyme reveal that FMN (flavin mononucleotide) is inaccessible to water radicals.

Topics: Bromides; Enzyme Activation; Free Radicals; Kinetics; L-Lactate Dehydrogenase; L-Lactate Dehydrogenase (Cytochrome); Potassium Compounds; Potassium Iodide; Saccharomyces cerevisiae; Solutions; Spectrometry, Fluorescence; Thiocyanates; Water

alpha-Chymotrypsin (alpha CT) was used as a model protein to study the effects of salt-induced precipitation on protein conformation. Process parameters investigated included the type and amount of salt used to induce precipitation. The salts studied included Na2SO4, NaCl, NaBr, KBr and KSCN. Precipitate secondary structure content was examined via laser Raman spectroscopy. Conventional and saturation transfer electron paramagnetic resonance spectroscopy were employed to probe the tertiary structure of the active site in spin-labelled alpha CT precipitates. As the molal surface tension increment of the inducing salt increased, the beta-sheet content increased and the alpha-helix content decreased. There was no significant variation in secondary structure with the amount of salt used. The fraction of precipitate that recovered activity on redissolution was correlated with the change in secondary structure content. Spin-labelled precipitate spectra indicated that the active site remains unaltered during precipitation. Molecular modelling was employed to investigate how physical property of alpha CT were affected by these types of conformational change. Estimated physical property changes could not account entirely for observed deviations from current equilibrium theory for salt-induced precipitation. The spectroscopic observations were also combined with activity/solubility results to propose a mechanism for the salt-induced precipitation of globular proteins.

Topics: Animals; Bromides; Chemical Precipitation; Chymotrypsin; Crystallography; Electron Spin Resonance Spectroscopy; Models, Molecular; Potassium; Potassium Compounds; Protein Conformation; Salts; Sodium; Sodium Chloride; Sodium Compounds; Spectrum Analysis, Raman; Structure-Activity Relationship; Sulfates; Thiocyanates

The influence of monovalent cations and anions on the structural parameters of dipalmitoylphosphatidylcholine (DPPC) bilayers was examined at 25 degrees C using X-ray diffraction. It was shown that monovalent salts, in general, have little effect on lipid packing within the bilayer. However, fully hydrated DPPC bilayers in 1 M KSCN pack in an interdigitated acyl chain phase. This is the first observation of an ion-induced interdigitated bilayer phase in a zwitterionic lipid. In addition, gel state DPPC bilayers in 1 M KBr imbibe approx. 10 A more solvent than bilayers in water. The influence of these same salts on the phase transitions of DPPC bilayers was also examined using high-resolution differential scanning calorimetry. These results are discussed in terms of ion-induced changes in solvent and solvent/bilayer structure.

Topics: 1,2-Dipalmitoylphosphatidylcholine; Bromides; Lipid Bilayers; Potassium; Potassium Compounds; Salts; Thermodynamics; Thiocyanates; X-Ray Diffraction

The effects of KSCN and other chaotropic salts on the androgen receptor in cytosol of Shionogi carcinoma 115 were studied by means of charcoal adsorption assay and sucrose gradient centrifugation. When KSCN or NaSCN was added to the [3H]-dihydrotestosterone-cytosol mixture at the final concentration of 0.5 M, the androgen binding to the cytosol receptor was considerably inhibited. The inhibition reached maximum within 5 h at 0 degrees C and was dependent on the kind of chaotropic anion added: the potency of inhibitory effect in descending order was KSCN greater than KI greater than KBr greater than KCl. The inhibition was not observed in the estradiol-receptor interaction with KSCN or NaSCN up to 0.5 M. When 0.5 M KSCN-treated androgen-cytosol mixture was subjected to gel filtration or (NH4)2SO4 fractionation to remove the salt, a partial recovery (30-40%) in specific binding activity was observed. The binding activity of androgen receptor was unaffected by a treatment with KSCN up to 0.1 M and the androgen-receptor complex sedimented in a 5S form in 0.1-0.3 M KSCN, 0.5 M KCl or 0.5 M KBr. These results suggest that the binding activity of androgen receptor is more susceptible than that of estrogen receptor to chaotropic salts which cause impairment in intramolecular hydrophobic interactions.

Topics: Adenocarcinoma; Animals; Bromides; Centrifugation, Density Gradient; Cytosol; Dihydrotestosterone; Male; Mice; Neoplasms, Experimental; Potassium; Potassium Compounds; Potassium Iodide; Receptors, Androgen; Receptors, Steroid; Thiocyanates