Klotz K H, Benz R
Lehrstuhl für Biotechnologie, Biozentrum der Universität Würzburg, Germany.
Biophys J. 1993 Dec;65(6):2661-72. doi: 10.1016/S0006-3495(93)81315-8.
Stationary and kinetic experiments were performed on lipid bilayer membranes to study the mechanism of iodine- and bromine-mediated halide transport in detail. The stationary conductance data suggested that four different 1:1 complexes between I2 and Br2 and the halides I- and Br- were responsible for the observed conductance increase by iodine and bromine (I3-, I2Br-, Br2I-, and Br3-). Charge pulse experiments allowed the further elucidation of the transport mechanism. Only two of three exponential voltage relaxations predicted by the Läuger model could be resolved under all experimental conditions. This means that either the heterogeneous complexation reactions kR (association) and kD (dissociation) were too fast to be resolved or that the neutral carriers were always in equilibrium within the membrane. Experiments at different carrier and halide concentrations suggested that the translocation of the neutral carrier is much faster than the other processes involved in carrier-mediated ion transport. The model was modified accordingly. From the charge pulse data at different halide concentrations, the translocation rate constant of the complexed carriers, kAS, the dissociation constant, kD, and the total surface concentration of charged carriers, NAS, could be evaluated from one single charge pulse experiment. The association rate of the complex, kR, could be obtained in some cases from the plot of the stationary conductance data as a function of the halide concentration in the aqueous phase. The translocation rate constant, kAS, of the different complexes is a function of the image force and of the Born charging energy. It increases 5000-fold from Br3- to I3- because of an enlarged ion radius.
在脂质双分子层膜上进行了静态和动力学实验，以详细研究碘和溴介导的卤化物运输机制。静态电导数据表明，I₂和Br₂与卤化物I⁻和Br⁻之间的四种不同的1:1配合物（I₃⁻、I₂Br⁻、Br₂I⁻和Br₃⁻）是碘和溴导致观察到的电导增加的原因。电荷脉冲实验有助于进一步阐明运输机制。在所有实验条件下，只能分辨出Läuger模型预测的三个指数电压弛豫中的两个。这意味着要么异质络合反应kR（缔合）和kD（解离）太快而无法分辨，要么中性载体在膜内始终处于平衡状态。在不同载体和卤化物浓度下的实验表明，中性载体的转运比载体介导的离子运输中涉及的其他过程快得多。因此对模型进行了修改。根据不同卤化物浓度下的电荷脉冲数据，通过单次电荷脉冲实验可以评估络合载体的转运速率常数kAS、解离常数kD和带电载体的总表面浓度NAS。在某些情况下，可以从静态电导数据作为水相中卤化物浓度的函数的图中获得络合物的缔合速率kR。不同络合物的转运速率常数kAS是镜像力和玻恩充电能的函数。由于离子半径增大，从Br₃⁻到I₃⁻它增加了5000倍。
