Gunn R B, Fröhlich O
J Gen Physiol. 1979 Sep;74(3):351-74. doi: 10.1085/jgp.74.3.351.
The kinetics of chloride and bromide transport were examined in intact human red blood cells and resealed ghosts. Because the influx and efflux of halide ions are almost equal (less than 0.01% difference), the stimulation of the exchange flux by external halides could be determined by measuring 36Cl or 82Br efflux. When the external halide concentration was increased by replacement of isoionic, isotonic solutions of sucrose and the nontransported anion citrate, the stimulation of the exchange flux was hyperbolic and was maximum at 20 mM halide externally. The K 1/2-out, the external concentration of chloride or bromide which stimulated the efflux to half of its maximum value, was 3 and 1 mM respectively, 15-fold smaller than K 1/2-in which we found to be about equal to the K 1/2 of halide self-exchange with nearly equal internal and external concentrations. Thus, the transport mechanism behaves asymmetrically with respect to these transported halides. Bromide flux was two-fold greater in bromide-chloride heteroexchange than in bromide-bromide self-exchange but it was still much smaller than the chloride self-exchange flux. The maximum influx and efflux of bromide in exchange for chloride were roughly eqal. Thus, since the maximum transport rates in the two directions are nearly equal, the kinetics of bromide equilibrium exchange with equal concentrations on the two sides are controlled on the inside where K 1/2 is greatest. The K 1/2-out Cl was a hyperbolic function of internal chloride concentration and was proportional to the maximum flux at each internal chloride concentration. These results are evaluated in terms of two broad categories of models. We conclude that, in contrast to other ion transport systems which have been shown to have kinetics of a sequential mechanism, anion exchange is compatible with a ping-pong mechanism in which a single site reciprocates between inside- and outside-facing orientations with asymmetric K 1/2 values.
在完整的人类红细胞和重封的血影中研究了氯离子和溴离子的转运动力学。由于卤离子的流入和流出几乎相等（差异小于0.01%），因此可以通过测量³⁶Cl或⁸²Br流出量来确定外部卤化物对交换通量的刺激作用。当通过替换等离子、等渗的蔗糖溶液和非转运阴离子柠檬酸盐来提高外部卤化物浓度时，交换通量的刺激作用呈双曲线，在外部卤化物浓度为20 mM时达到最大值。刺激流出量达到其最大值一半时的外部氯离子或溴离子浓度K₁/₂-out分别为3 mM和1 mM，比我们发现的K₁/₂-in小15倍，K₁/₂-in约等于卤化物在内部和外部浓度几乎相等时的自交换K₁/₂。因此，转运机制对于这些被转运的卤化物表现出不对称性。在溴离子-氯离子异向交换中，溴离子通量比溴离子-溴离子自交换中高两倍，但仍远小于氯离子自交换通量。溴离子与氯离子交换时的最大流入量和流出量大致相等。因此，由于两个方向上的最大转运速率几乎相等，两侧浓度相等时溴离子平衡交换的动力学在K₁/₂最大的内部受到控制。K₁/₂-out Cl是内部氯离子浓度的双曲线函数，并且与每个内部氯离子浓度下的最大通量成正比。根据两大类模型对这些结果进行了评估。我们得出结论，与已显示具有顺序机制动力学的其他离子转运系统不同，阴离子交换与乒乓机制兼容，在该机制中，单个位点在面向内部和面向外部的方向之间往复，具有不对称的K₁/₂值。
