Effect Of Ion Binding Research Articles

Spectroscopic and electrokinetic study of pH-dependent ionization of Langmuir-Blodgett films

The ionization of the spectroscopic probe molecule 4-heptadecyl-7-hydroxycoumarin (HHC) cast in Langmuir-Blodgett (L-B) films with the neutral diluent molecules poly(vinyl octadecyl ether) (PVOE) and octadecan-1-ol (OA) has been examined via the techniques of attenuated internal reflection spectroscopy and streaming potential measurements. For the HHC/PVOE system, cast onto fused silica made hydrophobic with octadecyltrichlorosilane (OTS), the anomalous titration results obtained earlier from this laboratory were confirmed by both techniques. A detailed theoretical examination, including consideration of the possible effects of ion binding, probe aggregation, and probe-substrate interactions, suggested that the most likely explanation of the HHC/PVOE results was that the OTS-treated surface was porous. For the HHC/OA system, cast onto fused silica made hydrophobic by esterification with dodecan-1-ol, the titration results were in agreement with the behavior predicted by the Gouy-Chapman equation and established a pK(a) of ca. 8.9 for HHC in the L-B film in the absence of any electrostatic potential from the probe/diluent film.

Effect of metal ion binding on the secondary structure of bovine .alpha.-lactalbumin as examined by infrared spectroscopy

We have examined the influence of monovalent and divalent cations on the secondary structure of bovine alpha-lactalbumin at neutral pH using Fourier-transform infrared spectroscopy. Our present studies are based on previously reported amide I' component band assignments for this protein [Prestrelski, S. J., Byler, D. M., & Thompson, M. P. (1991) Int. J. Pept. Protein Res. 37, 508-512]. The results indicate that upon dissolution, alpha-lactalbumin undergoes a small, but significant, time-dependent conformational change, regardless of the ions present. Additionally, these studies provide the first quantitative measure of the well-known secondary structural change which accompanies calcium binding. Results indicate that removal of Ca2+ from holo alpha-lactalbumin results in local unfolding of the Ca(2+)-binding loop; the spectra indicate that approximately 16% of the backbone chain changes from a rigid coordination complex to an unordered loop. We have also examined the effects of binding of several other metal ions. Our studies have revealed that binding of Mn2+ to apo alpha-lactalbumin (Ca(2+)-free), while inducing a small, but significant, conformational change, does not cause the alpha-lactalbumin backbone conformation to change to that of the holo (Ca(2+)-bound) form as characterized by infrared spectroscopy. Similar changes to those induced by Mn2+ are observed upon binding of Na+ to apo alpha-lactalbumin, and furthermore, even at very high concentrations (0.2 M), Na+ does not stabilize a structure similar to the holo form. Binding of Zn2+ to the apo form of alpha-lactalbumin does not result in significant backbone conformational changes, suggesting a rigid Zn(2+)-binding site.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of stretch‐activated ion channels in Xenopus oocytes.

1. The gating and permeation properties of endogenous stretch-activated (SA) ion channels in Xenopus oocytes have been studied using the patch-clamp single channel recording technique. 2. As estimated from the probability of being open (Po), SA channels were equally sensitive to suction or pressure. The Po was also weakly sensitive to voltage, increasing with depolarization. Channel activation did not require Ca2+. 3. Kinetic analysis of single-channel records indicated that there are three closed states and one open state. Among three closed-time distributions, the longest was the most sensitive to both pipette pressure and membrane voltage. The open time was independent of both pressure and voltage under a wide variety of ionic conditions, but was sensitive to the species of extracellular ion as follows: Na+ greater than Cs+ greater than K+ greater than Rb+ greater than Li+. The open time had a monotonic mole fraction relationship in mixtures of Li+ and K+. 4. The SA channels were cation-selective inward rectifiers. The selectivity for permeation, based on slope conductance, was: K+ greater than NH4+ greater than Cs+ greater than Rb+ greater than Na+ greater than Li+ greater than Ca2+. 5. Tetraethylammonium (TEA+) was impermeable but was not a channel blocker. 6.Open-channel current amplitude saturated with increasing extracellular K+, and was a monotonic function of the mole fraction of Li+ and K+ in mixtures of the two ions. 7. The channel has at least two separate ion binding sites: an intra-channel site suggested by the permeation data, and an allosteric site suggested by the voltage-independent effects of permeant ions on open time. A symmetric two-barrier, one-site model can quantitatively describe the permeation data. A kinetic model is proposed to quantify the gating kinetics and the effect of ion binding at the allosteric site.

Effects of ion binding and oily conditions on the adsorbed monolayer of crown ether compound at the oil/water interface

Effects of ion binding and oily conditions on the adsorbed monolayer of crown ether compound at the oil/water interface

Ion binding in polyelectrolyte solutions and the Poisson–Boltzmann equation

An improved analytical solution of the Poisson–Boltzmann equation for polyelectrolyte solutions containing simple salt is presented. By considering the small-ion distribution in the cell model in relation to the Donnan effect, ion binding in polyelectrolyte solutions is investigated. It is shown that the ion binding effect is a consequence of the non-uniform distribution of small ions in the solution and is of statistical origin. Theoretical predictions about the magnitude of the ion binding effect are in essential agreement with experimental observations.

On the specificity of the binding of cations to carrageenans: Counterion N.M.R. spectroscopy in mixed carrageenan systems

Counterion n.m.r. relaxation rates and signal intensities from mixed ion forms (sodium and rubidium) and mixed types (kappa and iota) of gel-forming carrageenans are presented. Data from the gel-promoting rubidium ion and the inert sodium ion obtained in the same mixed kappa-carrageenan systems indicate that only the rubidium ion binds to kappa-carrageenan and only in the gel state. Under non-gelling conditions, the transverse and longitudinal relaxation rates of sodium and the longitudinal relaxation rate of rubidium are independent of the ionic composition of samples of kappa-carrageenan. In systems containing mixed iota/kappa-carrageenan of the rubidium form, the large line-broadening effects observed for rubidium correlate with the kappa-carrageenan transition, which occurs in a temperature range well separated from that of the iota-carrageenan transition. The same conclusion holds for natural iota-carrageenan (from Euchema spinosa), where a small fraction of kappa-carrageenan is responsible for the large effects of ion binding observed in the rubidium relaxation.

Carbohydrate Complexes with Lead(II) Ion. Interaction of Pb(II) with β-d-Glucurono-6,3-lactone, d-Glucono-1,5-lactone, and Their Acid Anions and the Effects of Metal Ion Binding on the Sugar Hydrolysis

Abstract The interaction of Pb(II) ion with β-d-glucurono-6,3-lactone, d-glucuronic acid, d-glucono-1,5-lactone, and their acid anions has been investigated in aqueous solution and solid compounds of the type Pb(d-glucurono-6,3-lactone)(NO3)2, Pb(d-glucuronic acid)(NO3)2, Pb(II)–d-glucuronate, Pb(d-glucono-1,5-lactone)(NO3)2, and Pb(II)–d-gluconate have been isolated. These compounds are characterized by means of FT-IR, 1H and 13C NMR spectroscopy and molar conductivity measurements. Among these Pb–sugar complexes, the crystal structure of the Pb(II)–d-gluconate is known through X-ray diffraction measurements, in which the lead(II) ion is hexa-coordinated, binding to four d-gluconate anions via a carboxylato oxygen and an α-hydroxyl group of the two anions (chelation) and to a carboxylato oxygen atom of the other two sugar anions (unidentately). Spectroscopic evidence suggested that in the Pb–lactone or Pb–acid adducts, the metal ion could be bonded to a lactone or acid molecule through one of the carbonyl oxygen atom and other sugar donor group as well as to two bridging nitrato groups. In the Pb(II)–d-glucuronate, the metal ion could be bonded to four sugar moieties (similar to that of the Pb(II)–d-gluconate) via a carboxylato oxygen atom and other sugar donor group of the two anions and to a carboxylato oxygen atom of the other two acid anions, resulting into a hexa-coordinated lead(II) ion. The β-anomer sugar configuration is predominant in the free d-glucurono-6,3-lactone, d-glucuronic acid, d-glucuronate anion and in these Pb–sugar complexes.

Light-induced conductivity changes of purple membrane suspensions in strong electrolytes.

Measurements have been made of the modulated light-induced changes in conductivity and the associated relaxation times of bacteriorhodopsin in a variety of strong electrolytes, both unbuffered and buffered. The effects of pH and temperature variation have been studied as well as the effect of adding valinomycin. Two relaxation times can be distinguished: a fast lifetime associated with protonation-deprotonation, and a slow lifetime associated with ion binding. The ion-binding effects appear to be cation specific.

Cytochrome c: ion binding and redox properties. Studies on ferri and ferro forms of horse, bovine, and tuna cytochrome c.

The ion binding properties of horse, bovine, and tuna cytochrome c (both oxidized and reduced) have been measured using a combination of ultrafiltration, neutron activation, and ion chromatography. The ions investigated were chloride, phosphate, and Tris-cacodylate. Ion chromatography and neutron activation analysis techniques were employed to determine the concentration of free anions. Binding constants are obtained from modified Scatchard plots (in the range of 10-2000 M-1). The redox potentials for cytochrome c at different ionic strengths, pH 7.0, have been determined. In this paper we report the ionic strength and ion binding effects on the redox properties of horse, bovine, and tuna cytochrome c. Potential versus ionic strength dependence for horse, bovine, and tuna cytochrome c from the experimental data were compared with a theoretical model.

Carbohydrate-silver complexes. Interaction of β-D-glucurono-γ-lactone with Ag(I) ion and the effect of metal ion binding on sugar hydrolysis

The interaction of β-D-glucurono-γ-lactone (D- glucurone) with AgNO 3, AgClO 4, AgCH 3COO and Ag 2CO 3 has been studied in aqueous solutions and solid compounds of the type Ag(D-glucurone)NO 3· H 2O, Ag(D-glucurone)ClO 4·H 2O and Ag(D-glucuronate) have been synthesized and characterized by means of FT-IR spectroscopy, X-ray powder diffraction and molar conductivity. Spectroscopic and other evidence showed that in the Ag(D-glucurone)X·H 2O (X = NO 3 − or ClO 4 − complexes the silver(I) ion is two-coordinate, binding to a lactone carbonyl oxygen atom (O6) and to a nitrate or perchlorate oxygen atom, whereas the Ag(D-glucuronate) salt is dimeric with each Ag(I) ion bonded to two sugar anions via O6 and 6′ carboxyl oxygen atoms, resulting in a linear two- coordinate geometry around each silver ion. Silver nitrate and silver perchlorate stabilized the lactone domination, while silver acetate or silver carbonate facilitated the sugar-to-acid conversion and the ionization of the sugar moiety in aqueous solutions.

Thermodynamics of the hydrolysis of adenosine 5'-triphosphate to adenosine 5'-diphosphate.

The enthalpy of hydrolysis of the enzyme-catalyzed (heavy meromyosin) conversion of adenosine 5'-triphosphate (ATP) to adenosine 5'-diphosphate (ADP) and inorganic phosphate has been investigated using heat-conduction microcalorimetry. Enthalpies of reaction were measured as a function of ionic strength (0.05-0.66 mol kg-1), pH (6.4-8.8), and temperature (25-37 degrees C) in Tris/HCl buffer. The measured enthalpies were adjusted for the effects of proton ionization and metal ion binding, protonation and interaction with the Tris buffer, and ionic strength effects to obtain a value of delta H0 = -20.5 +/- 0.4 kJ mol-1 at 25 degrees C for the process, ATP4-(aq) + H2O(l) = ADP3-(aq) + HPO2-4(aq) + H+(aq) where aq is aqueous and l is liquid. Heat measurements carried out at different temperatures lead to a value of delta C0p = -237 +/- 30 J mol-1 K-1 for the above process.

Sugar-silver complexes. Interaction between the Ag(I) ion and D-glucono-δ-lactone and the effect of metal ion binding on sugar hydrolysis

Interaction between D-glucono-δ-lactone and the silver (I) ion has been studied in aqueous solution and solid compounds of the type Ag(D-gluconolactone)NO 3 · H 2O and Ag(D-gluconate) have been isolated and characterized. Spectroscopic properties and other chemical evidence suggested that the Ag(I) ion, in the Ag(D-gluconolactone)NO 3 · H 2O compound is two coordinated, binding to a sugar molecule via carbonyl oxygen atom and the nitrate group, whereas the Ag(D-gluconate) salt is a dimeric with each Ag(I) ion being bonded to the ionized 01 carboxyl oxygen atom of the first sugar anion and the carbonyl oxygen atom of the second sugar residue, resulting into a linear two coordination geometry around each silver ion. The strong intermolecular sugar hydrogen bonding network is rearranged upon silver interaction. The sugar hydrolysis is facilitated in aqueous solutions in the presence of Ag-acetate or Ag-perchlorate salts, while the AgNO 3 compound is stabilizing the lactone domination.

Divalent cation-induced phosphatidic acid membrane fusion. Effect of ion binding and membrane surface tension

A study was made on the correlation between the degree of membrane fusion and surface tension increase of phosphatidic acid membranes caused by divalent cations. Membrane fusion was followed by the Tb 3+ /dipicolinic acid assay, monitoring the fluorescent intensity for mixing of the internal aqueous contents of small unilamellar lipid vesicles. The surface tension and surface potential of monolayers made of the same lipids as used in the fusion experiments were measured as a function of divalent cation concentration. It was found that the ‘threshold’ concentration to induce massive vesicle membrane fusion was the same for Ca 2+ and Mg 2+, and that the surface tension increase in the monolayer, induced by changing divalent cation concentration from zero to a concentration which corresponds to its threshold value, inducing vesicle membrane fusion, was approximately the same: 6.3 dyn / cm for both Ca 2+ and Mg 2+. Both the divalent cation's threshold concentrations as well as the surface tension change corresponding to the threshold concentration for the phosphatidic acid membrane were smaller than those for the phosphatidylserine membrane. The different fusion capability of these divalent cations for phosphatidic acid and phosphatidylserine membranes is discussed in terms of the different ion binding capabilities of these ions to the membranes.

Demineralization and ion binding action of polycarboxylate cement liquid on human dental enamel.

The demineralization and ion binding effects on dental tissues due to poly(acrylic) acid attack under different dilution conditions of the latter are studied by scanning electron microscope (SEM) and infrared (IR) spectroscopy. The results indicate that in addition to the general demineralization effects such as preferential prism core attack, prism periphery attack, and protruding prism rods, competing ion binding effects also occur. Using optimum dilution conditions, the microstructural effects of demineralization and ion binding are shown and the effects are related to IR spectral observations.

Dielectric properties of quaternary ammonium ion-exchange beads dispersed in aqueous phases

Dielectric measurements were carried out for dense sediments of quaternary ammonium type anion-exchange resin beads dispersed in deionized water over a frequency range of 30 Hz to 130 MHz. According to a method proposed in previous studies the relative permittivities and electrical conductivities of ion-exchange beads were evaluated from the relaxation data observed in a megahertz region on the basis of a theory of interfacial polarization. The permittivities of the ion-exchange beads were found to be unchanged irrespectively of the salt form and somewhat lower than that of a continuous medium, while the conductivities of the ion-exchange beads were characteristic of the salt form. The equivalent ionic conductances of different counter anions in the beads were estimated from the conductivities of the ion-exchange beads. These results indicate an ion-binding effect in the resin beads.

Effect of carbohydrate and metal ion binding on the reactivity of the essential thiol groups of lima bean lectin.

A free sulfhydryl group previously has been shown to be required for carbohydrate binding to the lectin from lima bean (Phaseolus lunatus) (Gould, N. R. and Scheinberg, S. L. (1970) Arch. Biochem. Biophys. 141, 607-613). Modification of this group by sulfhydryl reagents was specifically inhibited by D-GalNAc. We have further examined the reactivity of sulfhydryl groups in lima bean lectin with 5,5'-dithiobis(2-nitrobenzoic acid) (Nbs2) as a probe for carbohydrate and metal ion binding. The 4 thiol groups in tetrameric lima bean lectin component III gave identical kinetics for reaction with Nbs2 involving formation of a weak noncovalent complex between Nbs2 and the lectin. The pH-independent reactivity of the thiol groups at neutral pH suggested that the thiols may exist as ion pairs with a nearby ionized group. Carbohydrate ligands were competitive inhibitors of thiol modification. The thiol groups on all 4 subunits of lima bean lectin were completely and reversibly protected by carbohydrate binding. The ability of carbohydrates to inhibit thiol modification correlated with their potency as inhibitors in a precipitin inhibition assay. The best inhibitors were the oligosaccharides alpha-D-GalNAc-(1 leads to 3)[alpha-L-fucose-(1 leads to 2)]beta-D-Gal(1 leads to R) and alpha-D-GalNAc-(1 leads to 2)beta-D-Gal(1 leads to R). Apparent thermodynamic parameters for binding of several carbohydrates were determined by measuring the temperature dependence of thiol protection. Removal of the bound metal ions Ca2+ and Mn2+ following dialysis into EDTA inactivated the lectin and increased the reactivity of the thiol groups 60-fold. This conversion was temperature-dependent and could be reversed upon addition of metal ions. The fast-reacting thiol groups were not protected by haptenic sugars from modifications by Nbs2.

Effects of monovalent ion binding and screening on measured electrostatic forces between charged phospholipid bilayers

In an effort to determine the role that monovalent ions play in the modification of intermembrane forces, we have measured these forces between charged phospholipid bilayers in monovalent ionic solutions. The osmotic stress technique allowed the net electrostatic pressure between the bilayers to be measured while their separation was concurrently determined by x-ray diffraction. Taken together, these measurements yielded electrostatic pressure as a function of bilayer separation. We have related measured pressures to the bilayer surface charge density and surface potential through an exact solution of the full nonlinear Poisson-Boltzmann equation for this system. Quantitative differences in bilayer separation amongst monovalent alkali metal cations indicated differential binding of these to phosphatidylglycerol (PG), phosphatidylserine (PS), and phosphatidic acid (PA); binding affinity series were determined for Li+, Na+, K+, Cs+, and TMA+ ions to these lipids. The anions Cl-, Br-, I-, and CH3COO- were found to have no differential effect on the repulsive forces between PS bilayers. Debye lengths for the electric double layer estimated from the slopes of the experimental pressure curves were consistently longer than predicted on the basis of classic Gouy-Chapman theory. Estimates of the van der Waals Hamaker coefficient between bilayers of PS and PG in salt solution were found to be weaker than between phosphatidylcholine bilayers in pure water, a difference possibly due to electromagnetic retardation and ionic screening.

Ion binding and micellar effects upon reactions of carboxylic anhydrides and carbonate esters

Ion binding and micellar effects upon reactions of carboxylic anhydrides and carbonate esters

Phosphorus-31 nuclear magnetic resonance studies of the methylene and fluoro analogues of adenine nucleotides. Effects of pH and magnesium ion binding.

The /sup 31/P NMR spectra of methylene and fluoro analogues of adenine nucleotides have been studied as a function of pH and Mg/sup 2 +/ concentration. As expected, the spectra of the fluoro analogues are not a function of pH. Mg/sup 2 +/ titrations show that both fluoro analogues bind the metal ion less strongly than ATP or ADP, respectively. For the analogues AMPPCP (..beta..,..gamma..) and AMPCP (..cap alpha..,..beta..), a pK/sub a/ near 8.1 was deduced for the titration of the terminal phosphoryl group; in the presence of Mg/sup 2 +/ this value is lowered to about 6.3. The other ATP analogue, AMPCPP (..cap alpha..,..beta..), has a titration behavior virtually identical with that of ATP. Therefore, at physiological pH all adenine nucleotides will be fully deprotonated in the presence of Mg/sup 2 +/ ions. A comparison of the magnitudes and directions of the chemical shift changes observed due to protonation leads to the conclusion that these are caused by changes in the structure of the polyphosphate chain. Mutual titrations indicate that both methylene ATP analogues can bind one Mg/sup 2 +/ tightly and a second ion more weakly. The methylene analogue of ADP binds only one Mg/sup 2 +/. Thesemore » data show that the methylene analogues compare favorably with ATP and ADP with respect to metal binding properties. A comparison of the results with those reported for imido- and thioadenine analogues suggests that the /sup 31/P NMR spectra for metal complexed nucleotides fee in solution are probably the fact-exchange average of all metal-coordination structures possible. This raises questions about the validity of direct comparisons of these spectra to those observed for enzyme-bound nucleotides. (JMT)« less

The Effects of Lipid Environment, Ion-Binding and Chemical Modifications on the Structure of the Gramicidin Transmembrane Channel

The weight-average mol wt was found to be 9,000, apparently themonomer of the DCCD-protein, suggesting that theconformation changes upon addition of DMSO. Small-angle x-ray scattering intensity curves obtained from theDCCD-proteinin watershowadiscreteinterferencemaxi-mumindicative of a considerable degree of regularity inthetwodimensional arrangementin theplaneperpendicu-lar to the DCCD-protein-axis. Awell-orientated diffrac-tion pattern of the DCCD-protein was obtained fromwhich cylindrically average intensity distribution curveswere calculated, revealing a