Unidirectional fluxes in saturated single-file pores of biological and artificial membranes. II. Asymptotic behavior at high degrees of saturation

A rate-theory analysis of isotope fluxes in filled single-file pores is given. It is assumed that the relation between the activities in solution and the fluxes can be described by the asymptotic laws for high activities. Only pore states containing no more than two vacancies need be taken into account. The flux-ratio exponent n, which is obtained by representing the ratio of unidirectional fluxes as a power of the electrochemical activity ratio, is found to provide information about m, the number of sites per pore. The general relation between n and m, for m ≥ 4, is m ? 3 ≤ n ≤ m ?1. For m = 2 or 3 the minimum value is 1. The theoretical results are discussed with respect to the internal structure of gramicidin pores in artificial bilayer membranes.