The Rate Constants of Valinomycin-Mediated Ion Transport through Thin Lipid Membranes |
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Authors: | G Stark B Ketterer R Benz and P Luger |
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Institution: | G. Stark, B. Ketterer, R. Benz, and P. Läuger |
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Abstract: | Electrical relaxation experiments have been performed with phosphatidylinositol bilayer membranes in the presence of the ion carrier valinomycin. After a sudden change of the voltage a relaxation of the membrane current with a time constant of about 20 μsec is observed. Together with previous stationary conductance data, the relaxation amplitude and the relaxation time are used to evaluate the rate constants of valinomycin-mediated potassium transport across the lipid membrane. It is found that the rate constants of translocation of the free carrier S and the carrier-ion complex MS+ are nearly equal (2·104 sec-1) and are of the same order as the dissociation rate constant of MS+ in the membrane-solution interface (5·104 sec-1). The equilibrium constant of the heterogeneous association reaction M+ (solution) + S (membrane) → MS+ (membrane) is found to be ~ 1 M-1, about 106 times smaller than the association constant in ethanolic solution. |
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