Kinetic analysis of carrier-mediated ion transport by the charge-pulse technique

Abstract

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.