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  • 1
    Electronic Resource
    Electronic Resource
    Role of Sterols in the Functional Reconstitution of Water-Soluble Mitochondrial Porins from Different Organisms (1995)
    s.l. : American Chemical Society
    Biochemistry 34 (1995), S. 3352-3361 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00010a026
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  • 2
    Electronic Resource
    Electronic Resource
    Structure of the squid axon membrane as derived from charge-pulse relaxation studies in the presence of absorbed lipophilic ions (1981)
    Springer
    The journal of membrane biology 59 (1981), S. 91-104 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Charge-pulse relaxation studies were performed on squid giant axons in the presence of membrane absorbed lipophilic anions, dipicrylamine (DPA) and tetraphenylborate (TPhB), and of specific blockers of sodium and potassium active currents. With the instrumentation used in this work a time resolution of 5 to 10 μsec was easily obtained without any averaging, although the voltage relaxations were always smaller than 5 mV in amplitude in order to keep the membrane voltage in a range where the used theory cyn be linearized. Two well distinguishable linear relaxations were invariably observed in the presence of the lipophilic anions. With DPA the fast relaxation (time constants between 8 and 70 μsec) was attributed to the redistribution of the lipophilic ions within the membrane following the change in membrane potential. The long relaxation process (time constant in the millisecond range) corresponds to the normal voltage relaxation of the passive squid axon membrane slightly modified by the process of redistribution of the extrinsic ions. The results support the same model for the translocation of lipophilic ions within the nerve membrane proposed earlier for artificial lipid bilayers. The fit of the data with a single barrier model yields the translocation rate constant,K, and the total concentration,N t , of membrane absorbed ions, from which the membrane-solution partition coefficient, β, can be derived. Both for DPA and TPhB,K had values close to those measured for solvent-free artificial lipid bilayers. The axon membrane appears as fluid mosaic membrane with a thickness of about 2.5 nm for the lipid bilayer part. In axons treated with DPA the dependence of relaxation data upon the holding membrane potential, $$\bar E_m$$ , provided information on the asymmetry of the membrane structure. The data were best fitted by assuming that nearly 100% of the membrane potential drops between the two free energy minima where the extrinsic ions are located, indicating that these minima lie very close to the membrane-solution interfaces, in the region of the phospholipid polar heads. The asymmetry voltage,E o, at which the extrinsic ions are expected to be equally distributed between the two sides of the membrane was found to range between −35 and −65 mV (inside negative), depending on the assumed shape of the free energy barrier describing the ion translocation process. This voltage is of the same sign and of the same order of magnitude as the equilibrium voltages for the open-close transitions of the gates of sodium and potassium channels, suggesting that all these voltages result from the same membrane asymmetry. A similar analogy was found between the asymmetry of the free energy barrier which best fitted DPA relaxation data and the asymmetrical voltage dependence of the gating of ionic channels. Our data were best fitted by assuming that about 70% of the potential drop occurs between the free energy minimum on the intracellular membrane face and the top of the barrier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01875707
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  • 3
    Electronic Resource
    Electronic Resource
    Structure of the axolemma of frog myelinated nerve: Relaxation experiments with a lipophilic probe ion (1981)
    Springer
    The journal of membrane biology 59 (1981), S. 127-134 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Asymmetrical displacement currents are measured in the absence and in the presence of the lipophilic anion dipicrylamine (DPA) in the extracellular solution of nerve fibres of the frogRana esculenta. DPA (30nM-3 μM) enhances the current by a component that has the properties expected for a translocation current of DPA ion across the lipid membrane. Analysis in terms of a single-barrier model yields the translocation rate constant (k), the total surface density of DPA absorbed to the membrane (N t ), and the equidistribution voltage (Ψ). The value ofk of about 104 s−1 is similar to that for a solvent-free artificial bilayer formed by the Montal-Mueller method. The surface densityN t varies with the DPA concentration as it does in the artificial bilayer, but is about tenfold smaller at all concentrations. The DPA ions sense an intrinsic electric field that is offset by a transmembrane voltage between 0 and 30 mV (inside positive). The part of the axolemma probed by the DPA ion appears as a thin (〈2.5 nm), fluid bilayer of lipids. DPA ions seem, however, to be excluded from the major part of the axolemma as if this area is occupied by integral proteins or negative charges.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01875710
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  • 4
    Electronic Resource
    Electronic Resource
    Optical and electrical properties of thin monoolein lipid bilayers (1985)
    Springer
    The journal of membrane biology 85 (1985), S. 181-189 
    Details
    ISSN: 1432-1424
    Keywords: lipid bilayer ; monoolein ; lipophilic ion ; ion carrier ; thickness ; dielectric constant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Monoolein lipid bilayers were formed using a monolayer transfer technique and from dispersions of monoolein in squalene, triolein, 1-chlorodecane and 1-bromodecane. Measurements of optical reflectance and electrical capacitance were used to determine the thickness and dielectric constant of the bilayers. The thickness of the hydrocarbon region of the five bilayer systems ranged from 2.5 to 3.0 nm. Two of the bilayer systems (made from 1-chlorodecane and 1-bromodecane solvents) had a high dielectric constant (2.8 to 2.9) whereas the other bilayer systems had dielectric constants close to that of pure hydrocarbons (2.2). The charge-pulse technique was used to study the transport kinetics of three lipophilic ions and two ion carrier complexes in the bilayers. For the low dielectric constant bilayers, the transport of the lipophilic ions tetraphenylborate, tetraphenylarsonium and dipicrylamine was governed mainly by the thickness of the hydrocarbon region of the bilayer whereas the transport of the ion-carrier complexes proline valinomycin-K+ and valinomycin-Rb+ was nearly independent of thickness. This is consistent with previous studies on thicker monoolein bilayers. The transport of lipophilic anions across bilayers with a high dielectric constant was 20 to 50 times greater than expected on the basis of thickness alone. This agrees qualitatively with predictions based on Born charging energy calculations. High dielectric constant bilayers were three times more permeable to the proline valinomycin-K+ complex than were low dielectric constant bilayers but were just as permeable as low dielectric constant bilayers to the valinomycin-Rb+ complex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871270
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  • 5
    Electronic Resource
    Electronic Resource
    Single-channel analysis of the conductance fluctuations induced in lipid bilayer membranes by complement proteins C5b-9 (1986)
    Springer
    The journal of membrane biology 94 (1986), S. 37-45 
    Details
    ISSN: 1432-1424
    Keywords: complement ; lipid bilayer ; membrane ; membrane pore ; membrane conductance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Single-channel analysis of electrical fluctuations induced in planar bilayer membranes by the purified human complement proteins C5b6, C7, C8, and C9 have been analyzed. Reconstitution experiments with lipid bilayer membranes showed that the C5b-9 proteins formed pores only if all proteins were present at one side of the membrane. The complement pores had an average single-channel conductance of 3.1 nS at 0.15m KCl. The histogram of the complement pores suggested a substantial variation of the size of the single channel. The linear relationship between single-channel conductance at fixed ionic strength and the aqueous mobility of the ions in the bulk aqueous phase indicated that the ions move inside the complement pore in a manner similar to the way they move in the aqueous phase. The minimum diameter of the pores as judged from the conductance data is approximately 3 nm. The complement channels showed no apparent voltage control or regulation up to transmembrane potentials of 100 mV. At neutral pH the pore is three to four times more permeable for alkali ions than for chloride, which may be explained by the existence of fixed negatively charged groups in or near the pore. The significance of these observations to current molecular models of the membrane lesion formed by these cytolytic serum proteins is considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01901011
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  • 6
    Electronic Resource
    Electronic Resource
    Alkali ion transport through lipid bilayer membranes mediated by enniatin A and B and beauvericin (1978)
    Springer
    The journal of membrane biology 43 (1978), S. 367-394 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Stationary conductance measurements with lipid bilayer membranes in the presence of enniatin A and B and beauvericin were performed. For comparison, some valinomycin systems were investigated. It was found that the conductance in the case of enniatin A and B is caused by a carrier ion complex with a 1∶1 stoichiometry, whereas for beauvericin, a 3∶1 carrier ion complex has to be assumed to explain the dependence of the conductance on carrier and ion concentration in the aqueous phase. The current-voltage curves measured with dioleoyl phosphatidylcholine membranes show a superlinear behavior for the three carriers in the presence of potassium. On the other hand, supralinear current-voltage curves were observed with membranes from different monoglycerides, except for beauvericin. The results obtained with enniatin A and B are in a satisfactory agreement with an earlier proposed carrier model assuming a complexation between carrier and ion at the membrane water interface. The discrimination between potassium and sodium ions is much smaller for the enniatins than for valinomycin. This smaller selectivity as well as the fact that potassium ions cause the highest conductance with lipid bilayer membranes may be due to the smaller size of the cyclic enniatin molecules, which contain 6 residues in the ringvs. 12 in the case of valinomycin. Charge-pulse relaxation studies were performed with enniatin A and B, beauvericin, and valinomycin. For monoolein membranes only in the case of valinomycin, all three relaxations predicted by the model could be resolved. In the case of the probably more fluid membranes from monolinolein (Δ9, 12-C18: 2) and monolinolenin (Δ9, 12, 15-C18: 3) for all carrier systems except for beauvericin, three relaxations were observed. The association rate constantk R , the dissociation rate constantk D , and the two translocation rate constantsk MS andk s for complexed and free carrier, respectively, could be calculated from the relaxation data. The carrier concentration in the aqueous phase had no influence on the rate constants in all cases, whereas a strong saturation of the association rate constantk R with increasing ion concentration was found for the enniatins. Because of the saturation,k R did not exceed a value of 4×105 m −1 sec−1 with 1m salt irrespective of carrier, ion, or membrane-forming lipid. A similar but less pronounced saturation behavior was also observed for the translocation rate constantk S of the free carrier. The other two rate constants were independent of the ion concentration in the aqueous phase. In the case of the enniatins, the translocation rate constantk MS was not independent from the kind of the transported ion. In the series K+, Rb+ and Cs+,k MS increases about threefold. The turnover numbers for the carriers as calculated from the rate constants range between 104 sec−1 and 105 sec−1 and do not show a strong difference between the individual carriers. The conductance difference in the systems investigated here is therefore mainly caused by the partition coefficients, which are smaller for the enniatins than for valinomycin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871697
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  • 7
    Electronic Resource
    Electronic Resource
    Determination of ion permeability through the channels made of porins from the outer membrane ofSalmonella typhimurium in lipid bilayer membranes (1980)
    Springer
    The journal of membrane biology 56 (1980), S. 19-29 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The three types of porin (matrix-proteins) fromSalmonella typhimurium with molecular weights of 38,000, 39,000 and 40,000 were reconstituted with lipid bilayer membranes either as a trimer or as an oligomer (complex I). The specific conductance of the membranes increased several orders of magnitude after the addition of the porins into the aqueous phase bathing the membranes. A linear relationship between protein concentration in the aqueous phase and membrane conductance was found. In the case of lower protein concentrations (10−12 m), the conductance increased in a stepwise fashion with a single conductance increment of 2.3 nS in 1m KCl. For a given salt the conductance increment was found to be largely independent of the particular porin (38 K, 39K or 40 K) and on the state of aggregation, although porin oligomers showed an up to 10 times smaller conductance increase in macroscopic conductance measurements. The conductance pathway has an ohmic current voltage characteristic and a poor selectivity for different alkali ions. Further information on the structure of the pores formed by the different porins fromSalmonella was obtained from the selectivity for various ions. From the permeability of the pore for large ions (Tris+, glucosamine+, Hepes−_ a minimum pore diameter of 0.8 nm is estimated. This value is in agreement with the size of the pore as calculated from the conductance data for 1m KCl (1.4 nm for a pore length of 7.5 nm). The pore diameter may well account for the sugar permeability which has been found in reconstituted vesicles. The findings reported here are consistent with the assumption that the different porins form large aqueous channels in the lipid bilayer membranes and that the single condutance unit is a trimer. In addition, it is suggested that one trimer contains only one pore rather than a bundle of pores.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869348
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  • 8
    Electronic Resource
    Electronic Resource
    Mechanism of sugar transport through the sugar-specific LamB channel ofEscherichia coli outer membrane (1987)
    Springer
    The journal of membrane biology 100 (1987), S. 21-29 
    Details
    ISSN: 1432-1424
    Keywords: LamB ; maltoporin ; lipid bilayer ; sugar transport ; transport mechanism ; membrane channel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Lipid bilayer experiments were performed with the sugar-specific LamB (maltoporin) channel ofEscherichia coli outer membrane. Single-channel analysis of the conductance steps caused by LamB showed that there was a linear relationship between the salt concentration in the aqueous phase and the channel conductance, indicating only small or no binding between the ions and the channel interior. The total or the partial blockage of the ion movement through the LamB channel was not dependent on the ion concentration in the aqueous phase. Both results allowed the investigation of the sugar binding in more detail, and the stability constants of the binding of a large variety of sugars to the binding site inside the channel were calculated from titration experiments of the membrane conductance with the sugars. The channel was highly cation selective, both in the presence and absence of sugars, which may be explained by the existence of carbonyl groups inside the channel. These carbonyl groups may also be involved in the sugar binding via hydrogen bonds. The kinetics of the sugar transport through the LamB channel were estimated relative to maltose by assuming a simple one-site, two-barrier model from the relative rates of permeation taken from M. Luckey and H. Nikaido (Proc. Natl. Acad. Sci. USA 77:165–171 (1980a)) and the stability constants for the sugar binding given in this study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02209137
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  • 9
    Electronic Resource
    Electronic Resource
    Transport of oppositely charged lipophilic probe ions in lipid bilayer membranes having various structures (1978)
    Springer
    The journal of membrane biology 44 (1978), S. 353-376 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A comparative study of the charge transport kinetics of oppositely charged lipophilic probe ions in lipid bilayer membranes of varying composition was carried out by using the charge pulse technique. The ions investigated were the chemical analogs tetraphenylborate, tetraphenylarsonium and tetraphenylphosphonium. Membrane structural aspects investigated were the type of solvent used in membrane formation, sterol content, and the nature of the principal lipid. The overall results indicate that the character of the transport process involving positive lipophilic probes is, in contrast to positively charged carrier complexes, very similar to that deduced in previous studies of negative lipophilic ions. The major effect on transport of lipophilic ions of both signs using differentn-alkane solvents appears to be due to changes in the thickness of the membrane hydrocarbon region. Positive ion transport is relatively sensitive to the inclusion of sterols of several types in both monoolein and lecithin membranes, as compared with negative ion transport, suggesting that a combination of sterol-induced dipolar field and fluidity changes are involved. Results involving several variations in lipid structure, with the possible exception of hydrocarbon tail saturation, when interpreted in terms of dipolar field changes deduced under the assumption of charge independent fluidity effects, are consistent with monolayer surface potential measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01944229
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  • 10
    Electronic Resource
    Electronic Resource
    The kinetic mechanism by which CCCP (carbonyl cyanidem-Chlorophenylhydrazone) transports protons across membranes (1984)
    Springer
    The journal of membrane biology 82 (1984), S. 179-190 
    Details
    ISSN: 1432-1424
    Keywords: chemiosmotic theory ; CCCP ; uncouplers ; protonophores ; bilayer membranes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary We demonstrate that a simple kinetic model describes the transport of protons across lipid bilayer membranes by the weak acid CCCP (carbonyl cyanidem-chlorophenylhydrazone). Four parameters characterize this model: the adsorption coefficients of the anionic and neutral forms of the weak acid onto the interface (β A andβ HA) and the rate constants for the movement of A− and HA across the membrane (k A andk HA). These parameters were determined by equilibrium dialysis, electrophoretic mobility, membrane potential, membrane conductance, and spectrophotometric measurements. From these equilibrium and steady state measurements on diphytanoyl phosphatidylcholine/chlorodecane membranes we found thatβ A=β HA=1.4 10-3cm,k A=175 s−1 andk HA=12,000 sec−1. These parameters and our model describe our kinetic experiments if we assume that the protonation reactions, which occur at the interfaces, remain at equilibrium. The model predicts a single exponential decay of the current in a voltage-clamp experimetn. The model also predicts that the decay in the voltage across the membrane following an intense current pulse of short duration (≈50 nsec) can be described by the sum of two exponentials. The magnitudes and time constants of the relaxations that we observed in both voltage-clamp and charge-pulse experiments agree well with the predictions of the model for all values of pH, voltage and [CCCP].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868942
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