Modification of valinomycin-mediated bilayer membrane conductance by 4,5,6,7-tetrachloro-2-methylbenzimidazole
Modification of valinomycin-mediated bilayer membrane conductance by 4,5,6,7-tetrachloro-2-methylbenzimidazole
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4,5,6,7-四氯-2-甲基苯并咪唑对缬氨霉素介导的双层膜电导的修饰
DOI：
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发表时间：
1976
影响因子：
2.4
通讯作者：
L. Bruner
中科院分区：
文献类型：
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作者：
K. Kuo;L. Bruner
摘要化合物4,5,6,7-四氯-2-甲基苯并咪唑（TMB）已被发现能显著改变缬霉素介导的钾离子通过脂质双分子层膜的稳态电导。TMB单独对膜电导率没有显著贡献，在溶液中呈电中性。在两类实验中的一类(I)中，首先将valinomycin添加到水相中，然后测量随着TMB逐步添加到水中膜电导的变化。在第二类实验（II）中，将valinomycin添加到成膜溶液中，然后将TMB添加到周围的水中。在这两种情况下，膜电导率都表现出随着TMB浓度的增加而增加，在较低的K+离子浓度下更为明显。当TMB浓度超过10−5m时，膜电导与K+离子浓度无关，而在TMB浓度低于10−7m时，膜电导与K+离子浓度呈线性关系。这种转变伴随着高场电流-电压特性从超线性（或弱次线性）到强次线性形式的变化。所有这些观察结果可能与Läuger和Stark （biochem）提出的载体药物转运动力学模型相关。Biophys。Acta211:458, 1970)，由此可以得出结论，在高TMB浓度下，缬霉素介导的离子转运受到未络合载体的反向扩散的限制。第一类实验显示，在高（bbb10−5m） TMB浓度下，电导急剧下降，这在第二类实验中没有出现，这是由于未络合载流子从水相进入受阻。最初在膜上的缬霉素通过向周围环体的横向扩散被清除。这种去除的时间依赖性已经在单独的一系列实验中进行了研究，导致在25°C下缬霉素的侧向扩散系数为5×10−6 cm2/sec。该值比相应的跨膜载体扩散系数大了两个数量级，进一步证明了缬霉素在膜/溶液界面的定位。
SummaryThe compound, 4,5,6,7-tetrachloro-2-methylbenzimidazole (TMB), has been found to markedly modify the steady-state valinomycin-mediated conductance of potassium (K+) ions through lipid bilayer membranes. TMB alone does not contribute significantly to membrane conductance, being electrically neutral in solution. In one of two classes of experiments (I), valinomycin is first added to the aqueous phases then changes of membrane conductance accompanying stepwise addition of TMB to the water are measured. In a second class of experiments (II), valinomycin is added to the membrane-forming solution, follwed by TMB additions to the surrounding water. In both cases membrane conductance shows an initial increase with increasing TMB concentration which is more pronounced at lower K+ ion concentration. At TMB concentrations in excess of 10−5m, membrane conductance becomes independent of K+ ion concentration, in contrast to the linear dependence observed at TMB concentrations below 10−7m. This transition is accompanied by a change of high field current-voltage characteristics from superlinear (or weakly sublinear) to a strongly sublinear form. All of these observations may be correlated by the kinetic model for carriermedicated transport proposed by Läuger and Stark (Biochim. Biophys. Acta211:458, 1970) from which it may be concluded that valinomycin-mediated ion transport is limited by back diffusion of the uncomplexed carrier at high TMB concentrations. Experiments of class I reveal a sharp drop of conductance at high (>10−5m) TMB concentration, not seen in class II experiments, which is attributed to blocked entry of uncomplexed carrier from the aqueous phases. Valinomycin initially in the membrane is removed by lateral diffusion to the surrounding torus. The time dependence of this removal has been studied in a separate series of experiments, leading to a measured coefficient of lateral diffusion for valinomycin of 5×10−6 cm2/sec at 25°C. This value is about two orders of magnitude larger than the corresponding coefficient for transmembrane carrier diffusion, and provides further evidence for localization of valinomycin in the membrane/solution interfaces.