Interaction Of Valinomycin Research Articles

Capillary affinity electrophoresis and ab initio calculation studies of valinomycin complexation with Na+ ion

In a combined experimental and theoretical approach, the interactions of valinomycin (Val), macrocyclic depsipeptide antibiotic ionophore, with sodium cation Na(+ )have been investigated. The strength of the Val-Na(+ )complex was evaluated experimentally by means of capillary affinity electrophoresis. From the dependence of valinomycin effective electrophoretic mobility on the sodium ion concentration in the BGE (methanolic solution of 20 mM chloroacetic acid, 10 mM Tris, 0-40 mM NaCl), the apparent binding (stability) constant (K(b)) of the Val-Na(+ )complex in methanol was evaluated as log K(b) = 1.71 +/- 0.16. Besides, using quantum mechanical density functional theory (DFT) calculations, the most probable structures of the nonhydrated Val-Na(+) as well as hydrated Val-Na(+).H(2)O complex species were proposed. Compared to Val-Na(+), the optimized structure of Val-Na(+).H(2)O complex appears to be more realistic as follows from the substantially higher binding energy (118.4 kcal/mol) of the hydrated complex than that of the nonhydrated complex (102.8 kcal/mol). In the hydrated complex, the central Na(+) cation is bound by strong bonds to one oxygen atom of the respective water molecule and to four oxygens of the corresponding C=O groups of the parent valinomycin ligand.

Theoretical and experimental study of the complexation of valinomycin with ammonium cation

The interactions of valinomycin, macrocyclic depsipeptide antibiotic ionophore, with ammonium cation NH4+ have been investigated. Using quantum mechanical density functional theory (DFT) calculations, the most probable structure of the valinomycin-NH4+ complex species was predicted. In this complex, the ammonium cation is bound partly by three strong hydrogen bonds to three ester carbonyl oxygen atoms of valinomycin and partly by somewhat weaker hydrogen bonds to the remaining three ester carbonyl groups of the valinomycin ligand. The strength of the valinomycin-NH4+ complex was evaluated experimentally by capillary affinity electrophoresis. From the dependence of valinomycin effective electrophoretic mobility on the ammonium ion concentration in the background electrolyte, the apparent binding (association, stability) constant (Kb) of the valinomycin-NH4+ complex in methanol was evaluated as log Kb = 1.52 +/- 0.22.

Selective ion-sensing based on Langmuir-Blodgett films having potential sensitive dyes. Effect of monolayer matrix on host-guest interaction of valinomycin with potassium ion

Abstract Surface pressure-area isotherms of anionic monolayers, arachidic acid and didodecylphosphate, containing valinomycin and a potential sensitive dye were measured on both KCl and NaCl subphases. The isotherm indicated that a phase separated cluster of valinomycin was formed in the arachidic acid monolayer. Fluorescence imaging of the surface monolayer with a newly constructed fluorescence microscope attached to a Langmuir film balance proved phase separation in the arachidic acid monolayer. The isotherm of arachidic acid on a KCl subphase was very similar to that on the NaCl subphase, but a small contraction was found on the KCl subphase. An isotherm of a valinomycin monolayer complexed with potassium ion, however, was more expansive than that for pure valinomycin. A large expansion in the isotherm observed in a mixed monolayer with didodecylphosphate suggested that valinomycin was homogeneously distributed in the fluid monolayer matrix. The isotherm on the KCl subphase was very different from that...

Interaction of valinomycin and stearic acid in monolayers

Surface pressure and surface potential as functions of surface area were measured for monolayers of valinomycin-stearic acid mixtures on the water-gas interface. Specific area per molecule of valinomycin, free energy of mixing, and dipole moment were calculated as a function of concentration of valinomycin. The s u m of the partial molecular areas in the mixture of valinomycin with stearic acid is significantly less than the calculated sum of the molecular areas of the pure components. This condensing effect is accompanied by two minima in free energy of mixing, valinomycin specific molecular area, and dipole moment, at low and high concentrations of valinomycin in mixed monolayers. Our data indicate that the miscibility of the valinomycin and the stearic acid in mixed monolayers is a function of composition. Langmuir-Blodgett deposited multilayer5 of mixed valinomycin-stearate monolayers were exposed to water solutions of KC1 and NaCl in a concentration range of 0.001-100 mM. The electric current generated by the monolayer system in contact with electrolyte solutions was dependent on KC1 concentration. In contrast, the system was not sensitive to Na+. The valinomycin-stearate multilayer thus has potential application as a potassium ion sensor.

Interaction of valinomycin and monovalent cations with the (Ca2+,Mg2+)-ATPase of skeletal muscle sarcoplasmic reticulum.

The interactions of monovalent cations and of the K+-specific ionophore, valinomycin, with the Ca2+-ATPase of skeletal muscle of sarcoplasmic reticulum have been studied in the absence of cation gradients by their effects on enzyme turnover and on the ATP plus Ca2+-dependent enhanced fluorescence of the ATP analogue, 2',3'-O-(2,4,6-trinitrocyclohexyldienylidine)-adenosine 5'-triphosphate (TNP-ATP) (Watanabe, T., and Inesi, G. (1982) J. Biol. Chem. 257, 11510-11516). Monovalent cations decreased turnover-dependent TNP-ATP fluorescence in the series K+ greater than Rb+ approximately equal to Cs+ greater than Na+ greater than Li+ (K0.5 = 49, 73, 75, 94, and 246 mM, respectively), consistent with the known specificity of the monovalent cation binding site that stimulates turnover and E-P hydrolysis. Valinomycin (200 nmol/mg), in the absence of monovalent cations, decreased ATPase activity by 30% and abolished the stimulatory effects of 150 mM KCl or NaCl on turnover. The ionophore alone enhanced TNP-ATP fluorescence by 20% and altered the specificity and affinity of the site that inhibited TNP-ATP fluorescence to Cs+ greater than Rb+ greater than K+ approximately equal to Na+ greater than Li+ (K0.5 = 79, 111, 134, 136, and 270 mM, respectively), which follows the Hofmeister series for effectiveness of monovalent lyotropic cations. TNP-ATP binding was not affected by either monovalent cations or valinomycin. Inhibition of turnover-dependent TNP-ATP fluorescence appears to be a useful parameter for monitoring monovalent cation binding to the Ca2+-ATPase. It is concluded that the ionophore interacts directly with the Ca2+-ATPase, independent of its K+ conductance effects on the lipid bilayer, and modifies the affinity and specificity of the monovalent cation site, either by direct interaction or by the formation of a valinomycin-monovalent cation-enzyme complex.

Interaction of valinomycin with electrolytes and lipids at the air/water interface

In accordance with other's data, valinomycin is very surface active. It spreads readily at the air/water interface, where it forms stable films and it penetrates lipid films. Surface potential measurements indicate that valinomycin films interact specifically with K + in preference to Na + in the absence of lipid. This interaction is favored by both high film pressure and high electrolyte concentration. Though smaller, definite differences between Na + and K + were observed also when valinomycin was spread on a lipid film preformed on dilute electrolyte solutions. In the absence of lipid, with low salt concentrations, up to 0.5 M (NaCl or KCl) in the subphase, no difference was seen between Na + and K + in either the force-area or the surface potential-area curves; upon compression of the valinomycin film the surface potential increased from 250 mV at 2 dyn/cm to 550 mV at 30 dyn/cm (collapse pressure), as much as on distilled water. With higher salt concentrations in the subphase, as the film pressure became greater than 20 dyn/cm, the surface potential ( ΔV) on KCl rose markedly above that on NaCl, the largest value of ΔV being 1050 mV on 0.7 M KCl and 1200 mV on 0.7 M KBr as compared with 550 mV on 0.7 M NaCl. When the chloride salts were used in the subphase the largest ΔV values (near collapse pressure) were in the order Li + < Na + « ⪡ K + > Rb + > Cs + > Ba 2+ > Mg 2+. At 10 dyn/cm the order was reversed to Rb + ⪢ K +. With K + salts, the largest ΔV values (near collapse) were in the order SO 4 2−, F − ⪡ Cl − < Br − > CNS − > I −; at high film pressure, K + was the most effective of the cations and Br − was the most effective of the anions. Demonstration of a specific valinomycin-K + interaction in the absence of lipid is in accordance with the view that valinomycin could function as a carrier molecule for K + across biological membranes. Since valinomycin does not contain any ionizable fixed charge, the surface potential effects observed with specific cations cannot be those of a Gouy diffused electrical double layer and represent a unique phenomenon in the interaction of ions with uncharged monolayers; this phenomenon has no counterpart in the literature of surface potentials and requires an explanation. A complex is proposed in which KCl or KBr are positioned as ± ion pairs across the II interface as to give the potential of a positive fixed charge; in a type of Stern layer, the K + is immobilized on the lipid side by the valinomycin binding site, and the anion is retained by the K + on the hydrophilic side.

Pigment containing lipid vesicles. II. Interaction of valinomycin with lecithin as sensed by chlorophyll a.

Valinomycin added to a suspension of chlorophyll a containing lecithin vesicles induces slight changes in the spectrum of chlorophyll a. These changes are measured as a difference spectrum between samples with and without valinomycin but of otherwise identical composition. The analysis of the experiments reveals that the effect is neither associated with the ionophoric properties of valinomycin nor due to a direct interaction of this agent with chlorophyll a. The molar ratio of valinomycin dissolved in the membrane to lecithin is found to be the relevant parameter, thus indicating an interaction between these two components. As a consequence, the aggregational state of the lecithin molecules is altered. Chlorophyll a incorporated into the membrane acts as a sensor, i.e. it reflects the alteration by a change in its spectroscopic parameters.

Interaction of valinomycin with cations at the air-water interface

A high surface potential is obtained when a valinomycin monolayer is spread upon a subphase containing KCl, RbCl or CsCl at concentration > 0.5 M . The observed selectivity pattern Rb + ⩾ K + > Cs + is the same as observed for valinomycin in bilayer conductance and partition experiments. Force-area curves of valinomycin at the air-water interface in the presence of 1.0 M K + or Rb + show a surface pressure transition that coincides with the rise in surface potential. This translation which is presumed to represent the association of valinomycin with the cation occurs at successively lower surface pressures as the cation concentration is increased. Collapse occurs at 165 Å 2 and 26–28 dynes/cm. In the absence of the cation, the force-area curve lacks the transition plateau and collapses at 24.5 dynes/cm and 185–190 Å 2. These data suggest that when valinomycin complexes a cation at the membrane-water interface, it undergoes a rearrangement that is evident from a decrease in surface area of approximately 20–25 Å 2.