PROTON TRANSPORT THROUGH MEMBRANES INDUCED BY WEAK ACIDS - STUDY OF 2 SUBSTITUTED BENZIMIDAZOLES
PROTON TRANSPORT THROUGH MEMBRANES INDUCED BY WEAK ACIDS - STUDY OF 2 SUBSTITUTED BENZIMIDAZOLES
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DOI：
10.1007/bf01868755
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发表时间：
1979-01-01
影响因子：
2.4
通讯作者：
MCLAUGHLIN, S
中科院分区：
文献类型：
--
作者：
DILGER, J;MCLAUGHLIN, S
本文报道了弱酸TTFB（4，5，6，7-四氯-2-三氟甲基苯并咪唑）质子跨磷脂双层膜的动力学研究。以前的动力学研究的同源5，6-二氯化合物，DTFB，表明质子易位的限速步骤是反扩散的中性，HA，形式的弱酸，这显然也是质子易位与TTFB的限速步骤。在高浓度的DTFB或TTFB下，带电的渗透物种类是图形 **。复杂.动力学分析和独立的测量结果表明，膜的渗透性HA和A-和HA的吸附系数是一个数量级高于DTFB TTFB。当DTFB或TTFB存在于pH小于弱酸pK的溶液中时，在施加电压阶跃时注意到电流的不寻常松弛。弛豫的幅度随着电压的增加而减小。这种松弛可能是由于在膜-溶液界面的苯并咪唑分子的重新取向。用DTFB在[大鼠肝脏]线粒体上进行实验。这些结果可以与双层数据和化学渗透假说的假设，线粒体膜的介电常数大于与癸烷作为溶剂形成的双层调和。为了证明介电常数对渗透性的影响，癸烷被1-氯癸烷代替。这使人工双层的电容增加了2倍，并且使双层对DTFB的A型的渗透性增加了2个数量级。
A kinetic study of the mechanism by which the weak acid TTFB (4,5,6,7-tetrachloro-2-trifluoromethylbenzimidazole) transports protons across phospholipid bilayer membranes was reported. A previous kinetic study of the homologous 5,6-dichloro compound, DTFB, revealed that the rate limiting step for proton translocation was the back diffusion of the neutral, HA, form of the weak acid; this was apparently also the rate limiting step for proton translocation with TTFB. At high concentrations of either DTFB or TTFB the charged permeant species was an .**GRAPHIC**. complex. The kinetic analysis and independent measurements revealed that the permeability of the membrane to HA and adsorption coefficients of A- and HA were an order of magnitude higher for TTFB than for DTFB. When either DTFB or TTFB was present in a solution where the pH was less than the pK of the weak acid, an unusual relaxation in the current was noted on application of a voltage step. The amplitude of the relaxation decreased as the voltage was increased. This relaxation was possibly due to a reorientation of the benzimidazole molecules at the membrane-solution interface. Experiments were performed with DTFB on [rat liver] mitochondria. These results could be reconciled with the bilayer data and with the chemiosmotic hypothesis by postulating that the dielectric constant of the mitochondrial membrane is greater than that of a bilayer formed with decane as a solvent. To demonstrate the effect of dielectric constant on permeability, decane was replaced by 1-chlorodecane. This increased the capacitance of the artificial bilayer by a factor of 2 and the permeability of the bilayer to the A- form of DTFB by 2 orders of magnitude.