Inabayashi M, Miyauchi S, Kamo N, Jin T
Laboratory of Biophysical Chemistry, Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
Biochemistry. 1995 Mar 14;34(10):3455-60. doi: 10.1021/bi00010a038.
Monensin is a polyether antibiotic ionophore and is considered an electroneutral Na/H antiporter. Its addition, however, increased the conductance of phospholipid bilayer membrane, and this increase was observed only when the medium contained Na+. Analysis of the current-voltage curve suggested that the increase was due to the formation and the translocation of an univalently charged species. The conductance at zero external voltage was proportional to the second power of monensin concentration and increased with the decrease in pH of the medium. Modified monensin whose terminal carboxyl was esterified showed much larger increase (ca. 100 times) in conductance than intact monensin. We concluded that the complex between the dimer of protonated monensin and Na+ contributed to the electrogenic transport of monensin. This complex bears a +1 charge, which is consistent with the analysis of current-voltage curves. Contrary to the conductance, the Na+ transfer rate of liposomal membrane measured with 23Na-NMR was proportional to the monensin concentration, meaning that the electrogenic component contributes little to the total monensin-mediated Na+ transport in the present system. It should be noted that this electrogenic component may change the membrane potential.
莫能菌素是一种聚醚类抗生素离子载体，被认为是一种电中性的Na⁺/H⁺反向转运体。然而，它的添加增加了磷脂双分子层膜的电导率，并且只有当介质中含有Na⁺时才观察到这种增加。电流-电压曲线分析表明，这种增加是由于单价带电物质的形成和转运。零外部电压下的电导率与莫能菌素浓度的二次方成正比，并随着介质pH值的降低而增加。末端羧基被酯化的修饰莫能菌素的电导率增加幅度比完整莫能菌素大得多（约100倍）。我们得出结论，质子化莫能菌素二聚体与Na⁺之间的复合物有助于莫能菌素的生电转运。该复合物带有+1电荷，这与电流-电压曲线分析一致。与电导率相反，用²³Na-NMR测量的脂质体膜的Na⁺转运速率与莫能菌素浓度成正比，这意味着在本系统中，生电成分对莫能菌素介导的总Na⁺转运贡献很小。应该注意的是，这种生电成分可能会改变膜电位。
