title: 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 musec 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 (2.10(4) sec(-1)) and are of the same order as the dissociation rate constant of MS(+) in the membrane-solution interface (5.10(4) sec(-1)). The equilibrium constant of the heterogeneous association reaction M(+) (solution) + S (membrane) --> MS(+) (membrane) is found to be approximately 1 M(-1), about 10(6) times smaller than the association constant in ethanolic solution.
mesh_terms: D000900:Anti-Bacterial Agents; D004553:Electric Conductivity; D007700:Kinetics; D008433:Mathematics; D008564:Membrane Potentials; D008567:Membranes, Artificial; D008956:Models, Chemical; D010539:Permeability; D010713:Phosphatidylcholines; D010716:Phosphatidylinositols; D011188:Potassium; D014634:Valinomycin
chemical_list: D000900:Anti-Bacterial Agents; D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D010716:Phosphatidylinositols; D014634:Valinomycin; D011188:Potassium