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  • 1975-1979  (9)
  • 1950-1954  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Ion transport and rotation of bacterial flagella (1977)
    [s.l.] : Nature Publishing Group
    Nature 268 (1977), S. 360-362 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Following Berg4 we assume that the S ring is attached to the peptidoglycan layer of the cell wall and that the M ring, which is mounted rigidly on the rod, is able to rotate in the plasma membrane (Fig. 1). We further assume that hydrogen ions which have in the extracellular medium a high ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/268360a0
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  • 2
    Electronic Resource
    Electronic Resource
    Photocurrents generated by bacteriorhodopsin on planar bilayer membranes (1979)
    Springer
    European biophysics journal 5 (1979), S. 277-292 
    Details
    ISSN: 1432-1017
    Keywords: Photocurrents ; Bacteriorhodopsin ; Lipid bilayer membranes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract When purple-membrane fragments from Halobacterium halobium are added to one aqueous phase of a positively-charged black lipid membrane, the membrane becomes photoelectrically active. Under normal conditions the steady-state photo-current is extremely low, but increases considerably when the lipid bilayer is doped with proton-permeable gramicidin channels or with a lipophilic acid-base system. These findings indicate that the purple-membrane sheets are bound to the surface of the bilayer, forming a sandwich-like structure. The time-behaviour of the photocurrent may be interpreted on the basis of a simple equivalent circuit which contains the conductance and capacitance of the purple membrane in series with the conductance and capacitance of the lipid bilayer. From the dependence of the photocurrent on the polarization of the exciting light the average angle between the transition moment of the retinal chromophore and the plane of the bilayer was calculated to be about 28 degrees. Furthermore, it was shown that chromophore-free apomembrane binds to the lipid bilayer and that its photoelectrical activity can be restored in situ by adding all-trans-retinal to the aqueous phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02426663
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  • 3
    Electronic Resource
    Electronic Resource
    Formation of ion channels by a negatively charged analog of gramicidin a (1977)
    Springer
    The journal of membrane biology 31 (1977), S. 171-188 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary O-pyromellitylgramicidin is a derivative of gramicidin in which three carboxyl groups are introduced at the terminal hydroxyl end of the peptide. Experiments with artificial lipid membranes indicate that this negatively charged analog forms ion-permeable channels in a way similar to that of gramicidin. If O-pyromellitylgramicidin is added to only one aqueous solution, the membrane conductance remains small, but increases by several orders of magnitude if the same amount is also added to the other side. In accordance with the dimer model of the channel, the membrane conductance under symmetrical conditions is proportional to the square of the aqueous concentration of O-pyromellitylgramicidin over a wide range. The ratioΜ PG/Μ G of the single-channel conductance of O-pyromellitylgramicidin to that of gramicidin is close to unity at high ionic strength, but increases more than fivefold at smaller ionic strength (0.01m). This observation is explained in terms of an electrostatic effect of the fixed negative charges localized near the mouth of the channel. In a mixture of O-pyromellitylgramicidin and gramicidin, unit conductance steps of intermediate size are observed in addition to the conductance steps corresponding to the pure compounds, indicating the formation of hybrid channels. Hybrid channels with preferred orientation may be formed if small amounts of gramicidin and O-pyromellitylgramicidin are added to opposite sides of the membrane. These hybrid channels show a distinct asymmetry in the current-voltage characteristic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869403
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  • 4
    Electronic Resource
    Electronic Resource
    Correlation analysis of electrical noise in lipid bilayer membranes: Kinetics of gramicidin A channels (1975)
    Springer
    The journal of membrane biology 20 (1975), S. 133-154 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary If a membrane contains ion-conducting channels which form and disappear in a random fashion, an electric current which is passed through the membrane under constant voltage shows statistical fluctuations. Information on the kinetics of channel formation and on the conductance of the single channel may be obtained by analyzing the electrical noise generated in a membrane containing a great number of channels. For this purpose the autocorrelation function of the current noise is measured at different concentrations of the channel-forming substance. As a test system for the application of this technique we have used lipid bilayer membranes doped with gramicidin A. From the correlation time of the current noise generated by the membrane, the rate constants of formation (k R ) and dissociation (k D ) of the channels could be determined. In addition, the mean square of the current fluctuations yielded the single-channel conductance Λ. The values ofk R ,k D , and Λ obtained from the noise analysis agreed closely with the values determined by relaxation measurments and single-channel experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870632
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  • 5
    Electronic Resource
    Electronic Resource
    Comments on: Correlation analysis of membrane noise (1976)
    Springer
    The journal of membrane biology 26 (1976), S. 407-407 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868887
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  • 6
    Electronic Resource
    Electronic Resource
    Kinetic analysis of carrier-mediated ion transport by the charge-pulse technique (1976)
    Springer
    The journal of membrane biology 27 (1976), S. 171-191 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The charge-pulse technique has been used previously for the study of quasistationary processes in membranes which required only a moderate time resolution. It is shown here that a time resolution of about 400 nsec may be achieved with this technique and that it may be applied to the kinetic analysis of carrier-mediated ion transport. By this method we have studied the transport of alkali ions through optically black monoolein membranes in the presence of the ion carrier valinomycin. All three relaxation processes that are predicted by theory have been resolved. From the relaxation times and the relaxation amplitudes the rate constants for the association (k R ) and the dissociation (k D ) of the ioncarrier complex, as well as the translocation rate constants of the complex (k MS ) and the free carrier (k S ) could be obtained. For 1m Rb+ at 25° C the values arek R =3×105 m −1 sec−1,k D =2×105 sec−1,k MS =3×105 sec−1,k S =4×104 sec−1. The activation energies of the single rate constants which have been estimated from experiments at two different temperatures range between 50 and 90 kJ/mol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869135
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  • 7
    Electronic Resource
    Electronic Resource
    Blocking of the gramicidin channel by divalent cations (1977)
    Springer
    The journal of membrane biology 35 (1977), S. 351-375 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The conductance of the gramicidin channel in the presence of alkali ions is strongly reduced when divalent cations such as Ca++ or Ba++ are added to the aqueous solutions in concentrations between 0.1 and 1m. Under the same conditions, carrier-mediated alkali ion transport is not affected by Ca++ and Ba++. Different divalent cations, differ considerably in their blocking action on the gramicidin channel; the effect of Mg++ or Zn++ is much smaller than that of Ca++ and Ba++. Besides reducing the single-channel conductance, the blocking ions also change the current-voltage characteristic of the channel from a nearly, linear to a strongly saturating behavior. These observations suggest that Ca++ or Ba++ (which are not permeable themselves) bind to a site at or near the channel mouth, thereby reducing the rate by which permeable ions enter and leave the channel. The blocking effect is analyzed in terms of the potential energy profile of the permeable ion in the channel. The saturating current-voltage characteristic may be explained by the assumption that in the presence of the blocking ion the passage over the entrance barrier is rate-limiting and, at the same time, only weakly voltage-dependent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869959
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  • 8
    Electronic Resource
    Electronic Resource
    Spectral analysis of current noise generated by carrier-mediated ion transport (1978)
    Springer
    The journal of membrane biology 41 (1978), S. 167-187 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary It is shown that valinomycin-mediated alkali ion transport is associated with a characteristic type of current noise. The spectral intensity of the noise which is measured under equilibrium conditions, i.e., at zero net current, is frequency independent (“white”) both at high and at low frequencies. The transition between the low- and the high-frequency limit occurs in a frequency range which is related to the characteristic relaxation time constants of the transport system. This behavior is predicted from the carrier transport model on the basis of Nyquist's theorem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01972631
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  • 9
    Electronic Resource
    Electronic Resource
    Electrical noise from lipid bilayer membranes in the presence of hydrophobic ions (1977)
    Springer
    The journal of membrane biology 37 (1977), S. 321-345 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary In the presence of the hydrophobic ion dipicrylamine, lipid bilayer membranes exhibit a characteristic type of noise spectrum which is different from other forms of noise described so far. The spectral density of current noise measured at zero voltage increases in proportion to the square of frequency at low frequencies and becomes constant at high frequencies. The observed form of the noise spectrum can be interpreted on the basis of a transport model for hydrophobic ions in which it is assumed that the ions are adsorbed in potential-energy minima at either membrane surface and are able to cross the central energy barrier by thermal activation. Accordingly, current-noise results from random fluctuations in the number of ions jumping over the barrier from right to left and from left to right. On the basis of this model the rate constantk i for the translocation of the hydrophobic ion across the barrier, as well as the mean surface concentrationN t of adsorbed ions may be caluculated from the observed spectral intensity of current noise. The values ofk i obtained in this way closely agree with the results of previous relaxation experiments. A similar, although less quantitative, agreement is also found for the surface concentrationN t .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01940938
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  • 10
    Electronic Resource
    Electronic Resource
    Über Dipyridyl-Metallkomplexe I. Metallionen und biologische Wirkung, 24. Mitteilung (1954)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 37 (1954), S. 1050-1052 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Exchange reactions in solutions containing Dipyridyl, Fe+2 and Cu+2 have been studied.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19540370411
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