Biophysical Journal 11: 981-994 (1971)
© 1971 the Biophysical Society

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The Rate Constants of Valinomycin-Mediated Ion Transport through Thin Lipid Membranes

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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