Interaction of Phospholipid and Antibiotic Ionophores, Gramicidin A' and Valinomycin, in Mixed Monolayers

抄録

To obtain information concerning the effects of ionophores on biological membranes, the thermotropic behavior of ionophores such as gramicidin A' and valinomycin in monolayers was investigated by measuring the surface pressure-area (π-A) and the surface viscosity-area (η_s-A) isotherms. Gramicidin A' had an isotherm having the treasition from a liquid-expanded through an intermediated to a condensed state, while valinomycin had a concave isotherm. The π-A isotherms for two ionophores had a decremental shift with increasing temperatures, depending upon a variety of their molecular structures. A distinict difference between the two ionophores in η_s-A isotherms was observed. In addition, the interaction of dimyristoylpho-sphatidylcholine (DMPC) with the two ionophores in mixed monolayers was investigated. When valinomycin was mixed with DMPC, no deviation from the additivity rule occurred below and above the phase transition temperature T_c of DMPC. However, when gramicidin A' was mixed with DMPC, a considerable negative deviation from ideal mixing occurred below T_c, suggesting the formation of an irregular ripple structure.