Conformational difference in cation complexes of tetranactin in solution

The conformational changes and binding behavior of tetranactin on complexation with sodium, potassium, rubidium, cesium, and ammonium ions were investigated by the measurements of proton magnetic resonance, ir, and Raman spectra. It has been clearly shown that alkali cations coordinate to the oxygen atoms of both the carbonyl group and the tetra-hydrofuran ring, but the ammonium ion coordinates only to the oxygen atom of the tetrahydrofuran. Among the alkali cations the potassium ion most strongly coordinates to the tetrahydrofuran oxygen atoms. The complexation with larger cations induces an expansion of the cavity of the macrocyclic ring of tetranactin and smaller cations contract the cavity. The evidence is revealed by the coupling constants of the methylene protons and the frequency separation between the carbonyl stretching vibrations of the ir- and Raman-active modes. The conformations of the cation complexes in the solid are maintained in solution but that of the cation free form is not.     

Cation exchange binding of rubidium and cesium by rat liver cell microsomes

The rubidium and cesium binding characteristics of rat liver cell microsomes were studied by an equilibration, centrifugation and washing procedure. Concentration dependence experiments, in which microsomes were equilibrated in media containing 0 to 400 mM rubidium or cesium chloride at pH 6.9, yielded saturation type adsorption isotherms similar to those previously reported for sodium and potassium. Mass law analysis of the data yielded apparent dissociation constants of 21 × 10^?3 eq/liter and 19 × 10^?3 eq/liter for rubidium and cesium binding, respectively. The results indicate that cesium is bound slightly more strongly than rubidium, and that both these cations may be bound more strongly than sodium or potassium. The maximum binding capacity at pH 6.9 was approximately 1.3 meq rubidium or cesium/g nitrogen. Sodium, potassium, magnesium and calcium generally associated with the isolated microsomes decreased concomitantly with increasing bound rubidium or cesium, demonstrating the ion exchange nature of the binding. Results of pH-dependence experiments showed that following equilibration of the microsomes in media containing approximately 96 mM rubidium or cesium at various pH values, bound rubidium or cesium was essentially zero at pH less than five, increased sharply between pH 5 and 7, and tended to level off at higher pH. The present results further characterize the cation binding properties of the microsomal material.     

Potassium transport system of Rhodopseudomonas capsulata

Rhodopseudomonas capsulata required potassium (or rubidium or cesium as analogs of potassium) for growth. These cations were actively accumulated by the cells by a process following Michaelis-Menten saturation kinetics. The monovalent cation transport system had Km's of 0.2 mM K+, 0.5 mM Rb+, and 2.6 mM Cs+. The rates of uptake of substrates by the potassium transport system varied with the age of the culture, although the affinity constant for the substrates remained constant. The maximal velocity of uptake of K+ was lower in aerobically grown cells than in photosynthetically grown cells, although the Km's for K+ and for Rb+ were about the same.     

7Li-NMR and FTIR studies of lithium, potassium, rubidium, and cesium complexes with ionophore lasalocid in solution

Lasalocid metal salts were combined with 1 : 1 lithium and 2:2 potassium, rubidium, and cesium to form complexes. The nature of the lasolocid salt complexes was studied in a solid and chloroform by FTIR spectroscopy in the middle and far IR regions. The process of the complexation of lithium was also studied by (7)Li-NMR. In chloroform a 1 : 1 complex of lasalocid and Li(+) ions was formed. Continuous absorption was observed in the far FTIR spectrum of this complex. It indicated large Li(+) polarizability, which was due to fast fluctuations of the Li(+) ions in the multiminima potentials, in the monomeric structure. In the lasalocid salt with the other monovalent cations (K(+), Rb(+), Cs(+)) 2:2 complexes were formed in which the cations showed cation polarizability, which strongly depended on the mass and the radius of the cations.     

Effects of nonsteroidal anti-inflammatory drugs on the uptake of various cations by lymphoid cells.

Several acidic nonsteroidal anti-inflammatory drugs (NSAID) as well as their corresponding alcohol molecules which are known to induce swelling of isolated lymphocytes by changing cell membrane permeability to water, are demonstrated also to induce changes of membrane permeability of lymphoid cells to one divalent cation, calcium, and to three monovalent cations, rubidium, cesium and sodium. According to the cells ionic environment, they increase or decrease the cellular uptake of cation which is itself also closely dependent on the ionic composition of the incubation medium. This drug-effect is very rapid, directly related to the medium NSAID concentration and almost totally reversible except to the most potent drugs such as flufenamic acid. Changes in intracellular ionic balance could have important catalytic effects on the metabolism of normal as well as of pathological cells. This fact could explain side-effects of these drugs as well as some of their therapeutic effects.     

DFT study of glucose based glycolipid crown ethers and their complexes with alkali metal cations Na+ and K+

A theoretical study of a series of five glucose based glycolipid crown ethers and their complexes with Na⁺ and K⁺ was performed using the density functional theory with B3LYP/6-31?G* to obtain the optimized geometrical structures and electronic properties. The local nucleophilicity of the five molecules was investigated using Fukui function, while the global nucleophilicity was calculated from the ionization potential and electron affinity. The structures and coordination of the complexes were studied to identify the best match of the glycolipid crown ethers with cations. In general, it was found that the oxygen atoms pairs O2 and O3 (or O4 and O6) on the sugar ring are constrained from moving toward the cation, which results in a weaker O-cation coordination strength for the oxygen pair compared to the other oxygen atoms in the crown ether ring. The thermodynamic properties of the binding of the complexes and the exchange reaction in gas phase were evaluated. The cation selectivity pattern among the five molecules was in good agreement with the experiment.     

Activation of the Escherichia coli cell division protein FtsZ by a low-affinity interaction with monovalent cations

We have investigated the activation of FtsZ by monovalent cations. FtsZ polymerization was dependent on the concentrations of protein and monovalent salts, and was accompanied by the uptake of a single ion per monomer added. The affinity and the specificity for the cation were low. Potassium, ammonium, rubidium or sodium activated FtsZ to different extents. Electron microscopy showed that polymers formed with either rubidium, or potassium, were very similar, as were their nucleotide turnover rates. The GTPase activity was lower with rubidium than with potassium, indicating that nucleotide exchange is independent of nucleotide hydrolysis. Control of polymerization by binding of a low affinity cation might govern the dynamic behavior of the FtsZ polymers.     

Monovalent-ion carrier effects on transport of Rb86 and Cs137 into bush bean plants

Summary Bush bean plants were exposed to either Rb⁸⁶ or Cs¹³⁷ for 24 hours with different monovalent cations as carriers in single-salt solutions except for the presence of 10⁻⁴ M CaCl₂. Ratio of uptake of the radionuclides at 10⁻³ to 10⁻² M was used as an index of the carrier ability of various cations. Different monovalent cations decreased uptake of Cs¹³⁷ and its transport to shoots unequally when 10⁻² M salts were compared with 10⁻³ M salts. Rubidium and cesium salts decreased Cs¹³⁷ uptake equally but potassium salts were less effective in decreasing uptake when the ratios of the two concentrations were considered. All monovalent cations decreased uptake of Cs¹³⁷ at the 10⁻² M carrier concentration but some did not at 10⁻³ M. Nitrate nitrogen was a big factor in these results. Cesium and rubidium salts were most effective. Potassium appeared to increase Cs¹³⁷ transport to shoots particularly at 10⁻³ M KNO₃. Only cesium, rubidium, and potassium salts decreased uptake of Rb⁸⁶ when 10⁻² M salts were compared with 10⁻³ M. Rubidium and cesium salts decreased uptake essentially equally and potassium salts again were less effective. All nitrate salts tended to increase Rb⁸⁶ transport to shoots more consistently than with Cs¹³⁷. It is concluded that absorption and transport to shoots were not equivalent for potassium, rubidium, and cesium.     

Crystal structures of valinomycin with potassium tetrachloroaurate and rubidium tetrachloroaurate with comparisons to other monovalent cation complexes

A total of 19 different crystal forms of complexes of valinomycin or its analogues with monovalent cations have been observed. The crystal structure determinations of valinomycin potassium tetrachloroaurate and valinomycin rubidium tetrachloroaurate are given here.Including this work complete structure determinations have now been published on 7 with 2 more soon to appear. Comparisons of these structural results suggest that the valinomycin complex opens at the D-valyl (lactyl) end and that contacts are possible between the complexed cation and other molecules. Such contacts may play an important part in membrane transport.     

Extracellular potassium dependency of block of HERG by quinidine and cisapride is primarily determined by the permeant ion and not by inactivation.

Drug induced Long QT syndrome results primarily from block of the cardiac potassium channel HERG (human-ether-a-go-go related gene). In some cases prolongation of the QT interval can result in the lethal arrhythmia torsade de pointes, an arrhythmia characterized by a rapid heart rate and severely compromised cardiac output. Many patients requiring medication present with abnormal serum electrolyte levels due to a variety of conditions including gastrointestinal dysfunction, renal and endocrine disorders, diuretic use, alcoholism, and aging. Extracellular cations have significant influence on HERG channel gating and in some instances they have been shown to alter drug block of HERG. However, the mechanisms by which drug block is altered in different extracellular cation solutions are not well understood. In this study, HERG block by quinidine and cisapride was assessed in extracellular solutions of calcium, potassium, rubidium, cesium, and tetraethylammonium (TEA) using two-electrode voltage clamping of Xenopus oocytes. Consistent with previous reports we show that increases in extracellular potassium reduce HERG block by quinidine and cisapride. We also show that increasing extracellular rubidium and cesium reduced HERG block by quinidine and cisapride whereas increasing extracellular calcium and extracellular TEA did not alter HERG block by quinidine and cisapride. These results demonstrate that at lower extracellular potassium concentrations, the permeant ion is almost exclusively responsible for the reduction in quinidine and cisapride block of HERG due to increases in extracellular potassium.     

Ionophore A23187: the effect of H+ concentration on complex formation with divalent and monovalent cations and the demonstration of K+ transport in mitochondria mediated by A23187.

The two-phase extraction technique has been used to study the equilibrium between A23187, metal cations, and H+. Under these conditions the ionophore forms charge neutral isostoichiometric complexes with divalent cations in which both carboxylate groups of the 2:1 A23187:M2+ complexes are deprotonated. In ethanol, however, the methyl ester of A23187 also binds divalent cations indicating that protonated complexes between A23187 and cations should also exist. With monovalent cations, A23187 forms two charge-neutral complexes of stoichiometries and relative stabilities: A2HM greater than AM. Examination of energy utilization K+ and H+ movements, and light scattering capacity of mitochondria in the presence of divalent cation chelators, A23187, and valinomycin demonstrates that A23187 can act as a nigericin type K+ ionophore under appropriate conditions. Formation constants for the A2HM complexes with monovalent cations indicate that with appropriate conditions transport of Li+ and Na+ mediated by A23187 would also be expected. The binding constant data and associated free energies of complex formation are compared as a function of ionic radius and of cation charge. The data indicate that lack of conformational mobility in A23187 is responsible for the high cation size selectivity of this compound. To explain the transport selectivity of A23187 for divalent cations, it is proposed that this ionophore forms a family of five complexes, isostoichiometric between cations of different valence but of which only charge-neutral species are permeant to membranes. The charge of a given complex is in turn determined by that of the cation. The concept is consistent with the divalent cation transport specificity of A23187, explains the observed monovalent cation transport, and is useful in rationalizing the differences in charge selectivity between A23187 and X-537A.     

The immediate uptake of potassium ion by mitochondria requiring gramicidin and 2,2-dimethylsuccinic anhydride.

The addition of 2,2-dimethylsuccinic anhydride to mitochondrial suspensions fortified with gramicidin and potassium ion but without any permeant anion caused an immediate and rapid increase in volume (as indicated by absorbance change at 520 nm) and the uptake of potassium ion (as indicated by a cation-specific electrode). The phenomena was not inhibited by rutamycin but was inhibited by either rotenone, antimycin or 2,4-dinitrophenol. Rotenone inhibition was relieved by succinate thus one of the requirements of the process was energy derived from endogenous substrates. Potassium ion could be replaced by rubidium and cesium ions but not by lithium or sodium ions. Since 2,2-dimethylsuccinate could not replace the anhydride and was not a permeant anion there must also be a requirement for the anhydride bond. The action of the anhydride on the mitochondria must be direct. Only closely related anhydrides were capable of engendering the effect of a highly effective permeant anion.     

Cation—π and Amino-Acceptor Interactions Between Hydrated Metal Cations and DNA Bases. A Quantum-Chemical View

Abstract

Cation—π interactions between cytosine and hexahydrated cations have been characterized using ab initio method with inclusion of electron correlation effects, assuming idealized and crystal geometries of the interacting species. Hydrated metal cations can interact with nucleobases in a cation—π manner. The stabilization energy of such complexes would be large and comparable to the one for cation—π complex with benzene. Further, polarized water molecules belonging to the hydration shell of the cation are capable to form a strong hydrogen bond interaction with the nitrogen lone electron pair of the amino groups of bases and enforce a pronounced sp³ pyramidalization of the nucleobase amino groups. However, in contrast to the benzene—cation complexes, the cation—π configurations are highly unstable for a nucleobase since the conventional in plane binding of hydrated cations to the acceptor sites on the nucleobase is strongly preferred. Thus, a cation—π interaction with a nucle-obase can occur only if the position of the cation is locked above the nucleobase plane by another strong interaction. This indeed can occur in biopolymers and may have an effect on the local DNA architecture. Nevertheless, nucleobases have no intrinsic propensity to form cation—π interactions.     

Purification and Characterization of an Alkaliphilic Choline Oxidase of Fusarium oxysporum

Uptake of cesium, potassium, and rubidium by Rhodococcus erythropolis CS98 and Rhodococcus sp. strain CS402 followed Michaelis-Menten saturation kinetics. The K_m’s for uptake of these monovalent cations by R. erythropolis CS98 and Rhodococcus sp. strain CS402 were 136 and 436μM for Cs⁺, 65 and 101μM for K⁺, and 102 and 113μM for Rb⁺, respectively. These values were significantly lower than those of Rhodobacter capsulatus and the Kup system in Escherichia coli. Potassium was a competitive inhibitor of cesium uptake by these strains, suggesting that cesium was accumulated by the potassium transport system. Although an uncoupler, FCCP, inhibited the cesium transport system, this system was not repressed by high concentrations of potassium in both Rhodococcus strains. However, the specificity in both Rhodococcus strains was different from the Trk system. These results suggest that the potassium transport system which can transport cesium in both Rhodococcus strains may be novel.     

Effects of external cesium and rubidium on outward potassium currents in squid axons

We have studied the effects of external cesium and rubidium on potassium conductance of voltage clamped squid axons over a broad range of concentrations of these ions relative to the external potassium concentration. Our primary novel finding concerning cesium is that relatively large concentrations of this ion are able to block a small, but statistically significant fraction of outward potassium current for potentials less than approximately 50 mV positive to reversal potential. This effect is relieved at more positive potentials. We have also found that external rubidium blocks outward current with a qualitatively similar voltage dependence. This effect is more readily apparent than the cesium blockade, occurring even for concentrations less than that of external potassium. Rubidium also has a blocking effect on inward current, which is relieved for potentials more than 20-40 mV negative to reversal, thereby allowing both potassium and rubidium ions to cross the membrane. We have described these results with a single-file diffusion model of ion permeation through potassium channels. The model analysis suggests that both rubidium and cesium ions exert their blocking effects at the innermost site of a two-site channel, and that rubidium competes with potassium ions for entry into the channel more effectively than does cesium under comparable conditions.     

Circular dichroism studies of salt- and alcohol- induced conformational changes in cyanophage S-2L DNA which contains amino 2 adenine instead of adenine.

DNA molecules containing AT pairs exhibit cesium cation specific conformational behavior. This specificity is shown to be cancelled with the title DNA, which not only concerns its conformational alterations in high-salt aqueous solutions but also the B-to-A transition induced by ethanol. S-2L DNA easily adopts the A-conformation in the presence of millimolar concentrations of CsCl which completely destabilize the A-conformation in calf thymus DNA. The present results demonstrate that the specific effects of cesium cations on DNA are connected with their binding to the AT pairs in the DNA minor groove.     

Chemical and ionization interferences in the atomic absorption spectrophotometric measurement of sodium,potassium, rubidium,and cesium

Although chemical and ionization interferences significantly affect the atomic absorption signal of the alkali metals, suitable corrective measures permit accurate analysis of these elements. The observed interferences are affccted in opposite ways by flame temperature, chemical depression of absorption produced by anions decreasing, and ionization enhancement produced by cations increasing with increasing flame temperature. Anionic depression is small in an acetylene-air flame and moderately large in a propane-air flame, increasing in the sequence sulfate < chloride < perchlorate < phosphate. Phosphate affects the cations in the order Na < K < Rb < Cs, with 20 mM phosphate depressing cesium absorbance approximately 40%. Conversely, ionization enhancement by cations is small in a propane-air flame and large in an acetyleneair flame, the effect on rubidium absorbance increasing in the sequence Mg < Ca < Li < Na < K < Cs, with 20 mM cesium producing a twoflod increase in absorbance. This is in the order of decreasing ionization potentials, indicating a direct relationship between ionization potential, degree of ionization, and enhancement produced. From consideration of the over-all effect of flame temperature on various interferences, we conclude that the propane-air flame is probably the most satisfactory for alkali metal analysis, especially for rubidium and cesium. Recovery studies on dialyzed and ashed rat liver microsomes and known controls demonstrate that addition of 15 mM lanthanum, to minimize anionic interferences, and addition of moderate concentrations of cesium, rubidium, or potassium, to minimize cationic enhancement, permit accurate and reliable measurement of the alkali metal cations in biological materials in the presence of potentially interfering cations and anions.     

Potassium and its role in cesium transport in plants

In plant cells, potassium (K⁺) is abundantly present and is dominant cation plays a vital role in maintaining physiological and morphological characteristics of plants. Many membrane integrated channels and transporters specific to K⁺ are involved in maintaining the potassium concentration within plants via membrane electrical activities. Elemental homologues to K⁺ compete with it for entry inside plants; among those, cesium is very common radionuclide. Once cesium enters into the plant cell, it can cause phytotoxicity. Therefore, it is desirable to understand complete pathway and mechanisms of cesium uptake in the plants, in order to assess consequences from accidental release of radioactive substance. This review focuses on mechanism of K⁺ ion uptake through channels/transporter and involvement of these channels/transporter in cesium uptake in plant cells.     

Ouabain-insensitive salt and water movements in duck red cells. I. Kinetics of cation transport under hypertonic conditions

Duck red cells in hypertonic media experience rapid osmotic shrinkage followed by gradual reswelling back toward their original volume. This uptake of salt and water is self limiting and demands a specific ionic composition of the external solution. Although ouabain (10(-4)M) alters the pattern of cation accumulation from predominantly potassium to sodium, it does not affect the rate of the reaction, or the total amount of salt or water taken up. To study the response without the complications of active Na-K transport, ouabain was added to most incubations. All water accumulated by the cells can be accounted for by net salt uptake. Specific external cation requirements for reswelling include: sufficient sodium (more than 23 mM), and elevated potassium (more than 7 mM). In the absence of external potassium cells lose potassium without gaining sodium and continue to shrink instead of reswelling. Adding rubidium to the potassium- free solution promotes an even greater loss of cell potassium, yet causes swelling due to a net uptake of sodium and rubidium followed by chloride. The diuretic furosemide (10(-3)M) inhibits net sodium uptake which depends on potassium (or rubidium), as well as inhibits net sodium uptake which depends on sodium. As a result, cell volume is stabilized in the presence of this drug by inhibition of shrinkage, at low, and of swelling at high external potassium. The response has a high apparent energy of activation (15-20 kcal/mol). We propose that net salt and water movements in hypertonic solutions containing ouabain are mediated by direct coupling or cis-interaction, between sodium and potassium so that the uphill movement of one is driven by the downhill movement of the other in the same direction.     

Polysaccharide sulfates. I. cellulose sulfate with a high degree of substitution

Previous methods for the sulfation of cellulose have a number of disadvantages among which excessive degradation and incomplete substitution are the most common. These disadvantages are overcome if a complex of sulfur trioxide with a neutral, highly polar compound, such as N,N-dimethylformamide, is used as the sulfating agent. For the sulfation of cellulose with this complex, any grade or type of cellulose is suitable. The resulting products usually have degrees of substitution greater than 2. The viscosities of their aqueous solutions are relatively high, indicating that degradation is minor. Two of the most interesting properties of this relatively undegraded cellulose sulfate are its reactivity with proteins and the gelation of its aqueous solutions to form thermoreversible gels in the presence of potassium, rubidium, or cesium ions. The properties are surprisingly similar to those of carrageenan, a polysaccharide sulfate occurring naturally in a number of red marine algae.