摘要：

In order to obtain information concerning the conformational features of cation-complexed ionophores on biological membranes, surface-pressure studies of the monolayers of ionophores, such as gramicidin A′ and valinomycin formed at an air/water interface, were carried out. The effect on the films when various salts were present in the subphase was also studied. At a concentration of 4 × 10−1 mol dm−3 the π–A isotherms for gramicidin A′ on all of the salts studied exhibited a maximal expansion in the condensed state. Based on the concentration dependence on the expansion of the gramicidin A′ monolayer, the efficiency of monovalent cations was found to be in the order NH4+ > K+ > Na+ > Li+. At a concentration of 4 × 10−1 mol dm−1, although the π–A isotherms for a valinomycin monolayer on KCl were indistinguishable from that on water at the liquid-expanded state, the π–A isotherms on LiCl, NaCl, and NH4Cl showed incremental shifts. On the other hand, by additional compression of a valinomycin monolayer on KCl over the plateau zone, an increase in the surface pressure appeared. However, the valinomycin monolayer on the other salts did not show such a behavior. This result indicates that valinomycin is specific for K+ in a membrane.

展开