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  • 1
    Electronic Resource
    Electronic Resource
    Current noise generated by electrogenic ion pumps (1984)
    Springer
    European biophysics journal 11 (1984), S. 117-128 
    Details
    ISSN: 1432-1017
    Keywords: Electrical noise ; membranes ; ion pumps ; active transport ; fluctuations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Active ion transport by ATP-or light-driven pumps involves a sequence of elementary steps such as binding and release of ions, as well as conformational transitions of the pump protein. At the microscopic level the individual reaction steps occur at random intervals, and therefore the current generated by electrogenic pumps fluctuates around a mean value. In this paper, a theoretical treatment of the electrical noise associated with active ion transport is given. The analysis, which is based on the calculation of the correlation function, yields the spectral intensity S 1 of current noise as a function of frequency, f. The shape of S I(f) contains information on the rate constants as well as on the magnitude of the charge displacements occuring during single reaction steps. The contribution of electrogenic pumps to the total voltage noise of the cell may be estimated from S I(f) and from the frequency-dependent impedance of the cell membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00276627
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    Paper (German National Licenses)
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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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    Paper (German National Licenses)
    Fulltext
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