Rapid Ion Exchange Research Articles

Activation of the glucocorticoid-receptor complex.

A crucial step in the interaction of glucocorticoids with target cells is the activation step, which involves a conformational change in the cytoplasmic glucocorticoid-receptor protein complexes and facilitates their binding to the cell nucleus. Activation can be quantified by measuring the ability of glucocorticoid-receptor complexes to bind to polyanions, such as DNA-cellulose, and unactivated complexes can be separated from activated complexes by rapid ion exchange chromatography using diethylaminoethyl (DEAE)-Sephadex or DEAE-cellulose. Activation occurs in vivo under physiological conditions and the rate of activation of cytoplasmic glucocorticoid-receptor complexes can be enhanced in vitro by physical manipulations (elevated temperature, increased ionic strength, dilution). In vitro studies suggest that activation is a regulated process and a low molecular weight component termed modulator, which has been identified in rat hepatic cytosol, inhibits activation. Additional studies employing phosphatase inhibitors, such as molybdate, and purified calf intestinal alkaline phosphatase suggest that either the receptor protein or a regulatory component is dephosphorylated during activation. Results obtained with specific chemical probes suggest that activation results in the exposure of basic amino acid residues consisting minimally of lysine, arginine, and histidine. Pyridoxal 5'-phosphate, a specific probe for lysine residues, exerts dual effects on glucocorticoid-receptor complexes, since it stimulates the rate of activation and also inhibits the binding of previously activated complexes to nuclei or DNA-cellulose. The ability of 1,10-phenanthroline, a metal chelator, to inhibit the DNA-cellulose binding of activated complexes suggests that a metal ion(s) located at or near the DNA binding site may become exposed as a consequence of activation. Collectively, the results of these various experiments suggest that activation is a regulated biochemical phenomenon with physiological significance.

Un nouveau conducteur protonique [H(H 2O) n] 12Sb 12O 36 (n ⩽ 1)

Single crystals of K 14Sb 12O 36F 2 undergo rapid ion exchange in 9N sulfuric acid to produce “hydronium” compound (H(H 2O) n) 12Sb 12O 36 (n ⩽ 1). Between 30 and 140°C this phase undergoes a partial and reversible dehydratation in which approximately 85 % of its “H 3O +” content is converted to H +. The structures of hydrated and dehydrated phases have been refined by full-matrix least squares, respectively to factor R = 0.030 and 0.047. The conductivity of (H(H 2O) n ) 12Sb 12O 36 (σ 20 ⋍ 1O 7 Ω −1cm −1 ) increases in an Arrhenius relationship with an activation energy of 8.8 kcal.mole −1, the dehydrated compound (H(H 2O) 0.33) 12Sb 12O 36 has a much lower conductivity but the same activation energy.

Cadmium-113 nuclear magnetic resonance investigation of metal binding sites in concanavalin A.

Cadmium-113 nuclear magnetic resonance studies are presented on the 113Cd-substituted protein concanavalin A (Con A). This protein has two different conformations, locked and unlocked, as described previously by Brown et al. [Brown, R. D., III, Brewer, C. F., & Koenig, S. H. (1977) Biochemistry 16, 3883]. The unlocked form of Con A gives one 113Cd resonance, indicating rapid exchange of the metal ions between the solution and the binding sites. Solutions of the locked form show three resonances: a free cadmium resonance (68 ppm), a resonance assigned to 113 Cd occupying the manganese site (46 ppm), and a resonance assigned to 113Cd occupying the calcium site (--125 ppm). In addition, Pb(II) is shown to bind to the calcium site and Zn(II) is shown to have high affinity for both sites. Data have been presented in previous literature that support a model in which Con A binds monosaccharides in a different manner than it binds oligosaccharides. However, if this difference exists, it does not affect the metal binding sites. Also, some heterogeneity in Con A has been reported in the literature; however, we have shown that the presence of these heterogeneities does not affect the 113 Cd NMR parameters.

THE IN VITRO SYNTHESIS OF GLYCINE BY RUMEN PAPILLAE

Following aerobic in vitro incubation of papillae from the ventral sac of the bovine rumen, amino acids released into the incubation medium were isolated using a rapid ion exchange procedure and measured quantitatively by gas-liquid chromatographic separation of the isobutyl-N(0)-heptafluorobutyryl esters. Of the potential precursors of the carbon skeleton of glycine that were added as substrates, only glyoxylate and serine (0.5–2 mM) resulted in enhanced glycine release while 10 mM glycolaldehyde, glycollate, glyoxal or oxalate or 1 mM monoethanolamine or hydroxyproline did not specifically influence glycine release. Each increase in glyoxylate concentration through 5, 10 or 20 mM caused an increased glycine release. In the presence of formate, inclusion of glycine as the added substrate increased serine release. Oxalate caused a non-specific release of amino acids. In the presence of glyoxylate, alanine and glutamate (1 mM) were effective precursors of the amino group of glycine.

A modified method for estimation of ornithine in biological samples

A rapid ion exchange chromatographic method was developed for the separation of tissue ornithine from other amino acids, except lysine, interfering with Chinard's ninhydrin method. The reaction was modified to estimate ornithine in the presence of lysine by reducing the color development time to 20 min and by benzene extraction of the chromogen formed. Chromogens of ornithine and lysine have 520 430 nm absorbance ratios of 4 and 1,3, respectively, and this was exploited to correct for lysine interference.

Radiochemical assays for creatine kinase and arginine kinase using rapid ion exchange separations

Simple and specific radiochemical assays for the determination of creatine and arginine kinase activities in crude tissue extracts are described. Creatine kinase is assayed by incubation with radioactive creatine and subsequent determination of the radioactivity in creatine phosphate. Creatine and creatine phosphate are separated on DEAE-cellulose ion exchange papers. Arginine kinase is assayed simllarly by using radioactive arginine and separating it from arginine phosphate on short ion exchange columns. An assay for creatine kinase in the direction of creatine formation is also described.

Hydronium beta″ alumina: A fast proton conductor

Single crystals of sodium beta″ alumina (0.84Na 2O·0.84MgO·5 Al 2O 3) undergo rapid ion exchange in concentrated sulfuric acid to produce “hydronium” beta alumina (0.84) H 2O·0.84MgO·5Al 2O 3·2.8H 2O). Hydronium beta″ alumina undergoes a partial, reversible dehydration between 250–300°C and irreversibly decomposes into alpha alumina and water above 700°C. The conductivity of hydronium beta″ alumina has been measured with blocking and non-blocking electrodes and is 5 × 10 −3 (ohm cm) −1 at 25°C. The high conductivity is interpreted on the basis of a two dimensional liquid model.

Impedance measurements using ionic contacts on purified and doped silver bromide crystals

Impedance measurements are made on purified, vacancy-doped and interstitial-doped silver bromide crystals of thicknesses from 0.061 cm to 0.260 cm using constant ionic strength solution contacts at temperatures from 20°C to 35°C. Results characterize the macroscopic transport properties from 316 kHz to 0.01 Hz and at d.c. In all cases the high frequency limit resistive component of the impedance, R ∞ , is equal to the d.c. resistance R 0 . This result indicates rapid ion exchange at the surfaces and neither Warburg diffusion nor surface kinetic-limitation of transport. As expected, R ∞ is a function of charge carrier concentration, which depends on extrinsic dopant concentration over the temperature range measured. For pure crystals the resistance, R ∞ , is linearly dependent on crystal thickness, δ, while thickness correlation could not be tested for the doped crystals as dopant level was not uniform. The geometric capacitance for all crystals, C g , is linear with δ −1 . The dimensionless dielectric constant, κ, calculated from C g and crystal dimentsions, is 13.9±0.7. The electric relaxation time, τ el , defined as the product R ∞ C g , at 25°C is found to be 50±3 μs for pure crystals, 1 to 4 μs for the Cd 2+ -doped crystals and 12 to 66 μs for the S 2− -doped crystals. Temperature dependance of R ∞ allows determination of crystal transport activation energies. For pure and Cd 2+ -doped crystals a value of 0.33±0.02 eV is found. For the S 2+ -doped crystals values from 0.48 to 0.28 eV are found. The parameter α, in the non-ideal Cole-Cole representation of impedance plane arcs, is 0.96±0.01 for purified crystals, 0.93±0.03 for Cd 2+ -doped, and 0.92±0.02 for S 2− -doped crystals.

Impedance measurements using ionic contacts on purified and doped silver bromide crystals

Impedance measurements are made on purified, vacancy-doped and interstitial-doped silver bromide crystals of thicknesses from 0.061 cm to 0.260 cm using constant ionic strength solution contacts at temperatures from 20°C to 35°C. Results characterize the macroscopic transport properties from 316 kHz to 0.01 Hz and at d.c. In all cases the high frequency limit resistive component of the impedance, R ∞, is equal to the d.c. resistance R 0. This result indicates rapid ion exchange at the surfaces and neither Warburg diffusion nor surface kinetic-limitation of transport. As expected, R ∞ is a function of charge carrier concentration, which depends on extrinsic dopant concentration over the temperature range measured. For pure crystals the resistance, R ∞, is linearly dependent on crystal thickness, δ, while thickness correlation could not be tested for the doped crystals as dopant level was not uniform. The geometric capacitance for all crystals, C g, is linear with δ −1. The dimensionless dielectric constant, κ, calculated from C g and crystal dimentsions, is 13.9±0.7. The electric relaxation time, τ el, defined as the product R ∞ C g, at 25°C is found to be 50±3 μs for pure crystals, 1 to 4 μs for the Cd 2+-doped crystals and 12 to 66 μs for the S 2−-doped crystals. Temperature dependance of R ∞ allows determination of crystal transport activation energies. For pure and Cd 2+-doped crystals a value of 0.33±0.02 eV is found. For the S 2+-doped crystals values from 0.48 to 0.28 eV are found. The parameter α, in the non-ideal Cole-Cole representation of impedance plane arcs, is 0.96±0.01 for purified crystals, 0.93±0.03 for Cd 2+-doped, and 0.92±0.02 for S 2−-doped crystals.

Determination of Arsenic, Antimony, Molybdenum, Thorium and Tungsten in Silicates by Thermal Neutron Activation and Inorganic ion Exchange

Abstract Ion exchange on Al2O3 columns has been used to quantitatively measure As, Sb, Mo, Th and W in silicate rocks. This procedure requires hour long thermal neutron irradiations, rapid ion exchange after the rocks are brought into solution by peroxide fusion, and short γ-ray counts on a Ge(Li) detector. Detection limits of 10 ppb have been achieved for As, Sb, Th and W. The best detection limit observed for Mo is 3 ppm.

Resolution of activated and unactivated forms of the glucocorticoid receptor from rat liver

Two forms of rat liver glucocorticoid receptor corresponding to the unactivated and activated states of the receptor were separated by rapid ion exchange chromatography on minicolumns of diethylaminoethyl (DEAE)-Sephadex and carboxymethyl (CM)-Sephadex. The more acidic form (D A) required a very high salt concentration to be eluted from DEAE-Sephadex and has not been reported previously. The identity of this form with the unactivated receptor which will not bind to CM-Sephadex (C A) was established. The more basic form (D B = C B), which was eluted at a lower salt concentration (0.18 m) from DEAE-Sephadex, could also bind to CM-Sephadex, indicating the presence of both positively and negatively charged regions on its surface. Since it was more easily eluted from CM-Sephadex than from DEAE-Sephadex, it was probably an acidic protein with a localized basic region. D A was converted to D B by heat and at 0 °C under the conditions associated with the Chromatographie procedure. The conversion was augmented in the presence of Tris buffer at higher pH but inhibited by phosphate buffer at a reduced pH.

Impedance measurements on purified silver chloride crystals using ionic vs. electronic contacts

Impedance measurements are made on purified silver chloride crystals covering thicknesses from 0.064 cm to 0.400 cm at temperatures from 293 K to 310 K using constant ionic strength solution contacts with varying silver ion concentrations. Results characterize the macroscopic transport properties from 10 kHz to 0.01 Hz and at d.c. Electrical relaxation times, τ el , are independent of crystal thickness and bathing solution composition, but dependent on temperature. The resistive component of the impedance, R ∞ , is linear with crystal thickness, δ , and the geometric capacitance, C g , linear with δ −1 . In agreement with Macdonald's theory, R ∞ is equal to the d.c. resistance, R 0 . This indicates rapid ion exchange at the surface and no Warburg diffusion. The dimensionless dielectric constant, calculated from C g and the crystal dimensions, is 15.4. An average activation energy of 0.298 eV, indicative of vacancy transport is found. The parameter α in the equivalent non-ideal Cole-Cole representation is 0.96 indicating a narrow distribution of time constants. These results are compared with the electronic contact measurements typical to solid state physics. Higher values of resistivity and lower values of C g and conductivity are found with graphite and vapor deposited silver. These differences were as large as 10%. Calculated dielectric constants at 10 kHz were 14.8 and 13.5, respectively, while the most recent published value is 11.14. These differences suggest that ionic solution contact measurements may give more reliable values because surface coverage is more nearly uniform on the molecular level.

Impedance measurements on purified silver chloride crystals using ionic vs. electronic contacts

Impedance measurements are made on purified silver chloride crystals covering thicknesses from 0.064 cm to 0.400 cm at temperatures from 293 K to 310 K using constant ionic strength solution contacts with varying silver ion concentrations. Results characterize the macroscopic transport properties from 10 kHz to 0.01 Hz and at d.c. Electrical relaxation times, τ el, are independent of crystal thickness and bathing solution composition, but dependent on temperature. The resistive component of the impedance, R ∞, is linear with crystal thickness, δ, and the geometric capacitance, C g , linear with δ −1. In agreement with Macdonald's theory, R ∞ is equal to the d.c. resistance, R 0. This indicates rapid ion exchange at the surface and no Warburg diffusion. The dimensionless dielectric constant, calculated from C g and the crystal dimensions, is 15.4. An average activation energy of 0.298 eV, indicative of vacancy transport is found. The parameter α in the equivalent non-ideal Cole-Cole representation is 0.96 indicating a narrow distribution of time constants. These results are compared with the electronic contact measurements typical to solid state physics. Higher values of resistivity and lower values of C g and conductivity are found with graphite and vapor deposited silver. These differences were as large as 10%. Calculated dielectric constants at 10 kHz were 14.8 and 13.5, respectively, while the most recent published value is 11.14. These differences suggest that ionic solution contact measurements may give more reliable values because surface coverage is more nearly uniform on the molecular level.

A spiral ion exchanger for rapid radiochemical separations

A new rapid ion exchange method for separating elements has been developed. The method is best suited to separating small amounts of substances and carrier-free radioisotopes. In a normal ion exchange, separation times of ten seconds are easily obtainable. In cases where short-lived daughter products have to be separated from long-lived parent substances, separation times as low as 10 ms are achievable.

Determination of arsenic, tungsten, and antimony in natural waters by neutron activation and inorganic ion exchange.

Ion exchange on Al/sub 2/O/sub 3/ columns has been used to quantitatively measure As, Sb, and W in water. This procedure requires short thermal neutron irradiations; rapid ion exchange without chemical manipulations, and short ..gamma..-ray counts on a Ge(Li) detector. Precisions of +-5% can be routinely obtained and the following detection limits have been achieved: As, 0.05 ppb; Sb, 0.03 ppb; and W, 0.05 ppb.

The binding of CO2 to human hemoglobin.

CO2-dissociation curves of concentrated human deoxy- and carbonmonoxyhemoglobin at 37 degrees, pH 7.6 to 7.0, PCO2 equal to 10 to 160 mm Hg, have been obtained by a rapid mixing and ion exchange technique. The CO2-dissociation curves for deoxyhemogloblin can only be fitted by assuming two classes of binding sites for carbon dioxide. The simplest way to account for the experimental data is to assume that the alpha-amino groups of the alpha and beta chains react with carbon dioxide with affinities that differ by at least a factor of 3. No difference in reactivity with CO2 was found among the four terminal alpha-amino groups of carbonmonoxyhemoglobin.

A rapid ion exchange method for quantitation of the urinary excretion of 3-methylhistidine

A simple accelerated ion exchange chromatographic method has been described for the estimation of 3-methylhistidine in urine and plasma. The system uses a column of 7% cross-linked cation exchange resin with one buffer (pH 3.98) and one temperature (30°C). A human urine sample is applied directly (pH 2.2) to the column and its 3-methylhistidine concentration is determined in less than one hour.

Determination of Selenium in Natural Waters Using the Centrifugal Photometric Analyzer

Abstract A rapid ion exchange separation converts the methylene blue spot test for selenium into a selective and sensitive method for quantitative determination of trace quantities of selenium. Increased speed, accuracy, and reproducibility is achieved because of the parallel analysis technique of the centrifugal photometric analyzer (GeMSAEC Fast Analyzer). Natural water samples, spiked with 0.10 to 0.5 μg of selenium, were analyzed with an average accuracy of 4.2 % after removal of interferences by ion exchange.

Accessibility of the central nervous connectives of Anodonta cygnea to a compound of large molecular weight.

ABSTRACTUltrastructural observations on the uptake of an exogenous tracer substance, horseradish peroxidase (M.W. 40,000), have shown that this large molecule can penetrate the neural lamella in intact cerebro-visceral connectives of the lamellibranch, Anodonta cygnea. Peroxidase molecules were also observed to penetrate between the intercellular clefts formed by adjacent membranes of the underlying peripheral glial cell layer and to move extensively into the underlying extracellular spaces. These observations confirm the results of previous electrophysiological, radio-isotopic and ultrastructural investigations indicating that a relatively rapid exchange of water-soluble ions and molecules occurs between the blood, or bathing medium, and the extracellular fluid bathing the axon surfaces in intact connectives.

Dissolution kinetics of magnesium silicates

Kinetic dissolution experiments on serpentine, forsterite and enstatite over a wide pH range at 25°C show that there is an initial rapid exchange of surface magnesium ions with hydrogen ions followed by a longer period of hydrogen exchange and extraction of internal magnesium and silicon, with the amount extracted proportional to t 1 2 . The parabolic exchange kinetics are consistent with either of two rate controlling mechanisms: nonsteady state diffusion of ions within the mineral and quasi-steady state diffusion of ions through a leached shell surrounding the mineral. Diffusion coefficients for magnesium are greater than for silicon for each of the minerals, leading to incongruent dissolution over moderate time periods. The diffusion coefficients decrease in the order forsterite > serpentine > enstatite. Eventually the parabolic exchange rates decrease to the rate of dissolution of all material at the aqueous interface. Hence, over very long periods the amount of silicon and magnesium dissolved is proportional to t and dissolution is congruent. In highly acid solutions dissolution rates are fast and this terminal condition is reached much sooner.