Abstract：
A quantitative description of ionophore-mediated ion transport is important in understanding ionophore activity in biological systems and developing ionophore applications. Herein, we describe the direct measurement of the electrical current resulting from K+ transport mediated by individual valinomycin (val) ionophores. Step fluctuations in current measured across a 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) bilayer suspended over a ∼400 nm radius glass nanopore result from dynamic partitioning of val between the bilayer and torus region, effectively increasing or decreasing the total number of val present in the membrane. In our studies, approximately 30 val are present in the membrane on average with a val entering or leaving the bilayer approximately every 50 s, allowing measurement of changes in electrical current associated with individual val. The single-molecule val(K+) transport current at 0.1 V applied potential is (1.3 ± 0.6) × 10-15 A, consistent with estimates of the transport kinetics based on large val ensembles. This methodology for analyzing single ionophore transport is general and can be applied to other carrier-type ionophores.
摘要：
离子载体介导的离子运输的定量描述对于理解生物系统中的离子载体活性和开发离子载体应用非常重要。在这里，我们描述了由单个缬氨酸霉素（val）离子载体介导的K转运产生的电流的直接测量。在一个1,2-二植酸酰-sn-甘油-3-磷酸胆碱（DPhPC）双层中测量的电流的阶跃波动悬浮在一个~400nm半径的玻璃纳米孔上，是由于双层和环面区域之间val的动态分配导致的，有效地增加或减少膜中存在的val的总数。在我们的研究中,膜中平均存在大约30val，大约每50s有一个val进入或离开双层，允许测量与个体VAL相关的电流变化。在施加0.1V的电势下，单分子val（K）传输电流为（1.3±0.6）×10-15A，与基于大val合奏的运输动力学估计一致。这种分析单离子载体运输的方法是通用的，可以应用于其他载体型离子载体。
