Kenney L J, Kaplan J H
Department of Physiology, School of Medicine, University of Pennsylvania, Philadelphia 19104-6085.
J Biol Chem. 1988 Jun 15;263(17):7954-60.
The sodium pump of human red blood cells mediates a Rb:Rb exchange that is dependent for maximal rates upon the simultaneous presence of intracellular ATP (or ADP) and phosphate. We have measured ouabain-sensitive 86Rb uptake into resealed ghosts of human red cells containing ADP and show that arsenate will substitute for phosphate in supporting the Rb:Rb exchange transport mode. The concentration dependence of arsenate-supported Rb:Rb exchange in ghosts containing 2 mM ADP shows both activating and inhibiting phases; the dependence upon phosphate shows similar characteristics. Elevation of the external [Rb] lowers the apparent affinity for arsenate since there is a shift to higher concentrations of arsenate in the activating and inhibiting phases of the arsenate concentration dependence curve. Similarly, elevation of [ADP] substantially reduces the inhibition of Rb:Rb exchange observed at higher [arsenate]. These effects are also observed in phosphate-supported Rb:Rb exchange. The phosphate requirement for Rb:Rb exchange involves phosphorylation of the sodium pump protein; the close agreement between the effects of arsenate and phosphate in supporting Rb:Rb exchange makes it likely that arsenylation of the sodium pump occurs during Rb:Rb exchange. Arsenate efflux from red blood cell ghosts into arsenate-free chloride medium is partially inhibited (77-80%) by DNDS (4,4'-dinitro-2,2'-stilbenedisulfonic acid), this compares with 82-87% inhibition by DNDS of phosphate efflux under the same conditions. It appears that Band III, the red cell anion transport system, accepts arsenate in a similar fashion to phosphate and that a fraction of the flux of both anions may occur through pathways other than Band III. Thus, in human red blood cells, both the sodium pump and the anion exchange transport system will accept arsenate as a phosphate congener and the protein-arsenate interactions are very similar to those with phosphate.
人类红细胞的钠泵介导了一种铷（Rb）:铷交换，其最大速率依赖于细胞内ATP（或ADP）和磷酸盐的同时存在。我们测量了含有ADP的人红细胞重封膜囊泡中哇巴因敏感的⁸⁶Rb摄取，并表明砷酸盐在支持Rb:Rb交换转运模式方面可替代磷酸盐。在含有2 mM ADP的膜囊泡中，砷酸盐支持的Rb:Rb交换的浓度依赖性呈现出激活和抑制阶段；对磷酸盐的依赖性也显示出类似特征。外部[Rb]的升高降低了对砷酸盐的表观亲和力，因为在砷酸盐浓度依赖性曲线的激活和抑制阶段，会向更高浓度的砷酸盐转变。同样，[ADP]的升高显著降低了在较高[砷酸盐]时观察到的对Rb:Rb交换的抑制作用。在磷酸盐支持的Rb:Rb交换中也观察到了这些效应。Rb:Rb交换对磷酸盐的需求涉及钠泵蛋白的磷酸化；砷酸盐和磷酸盐在支持Rb:Rb交换方面的效应密切一致，这使得钠泵在Rb:Rb交换过程中可能发生砷酰化。从红细胞膜囊泡向无砷酸盐的氯化物培养基中的砷酸盐外流被4,4'-二硝基-2,2'-二苯乙烯二磺酸（DNDS）部分抑制（77 - 80%），相比之下，在相同条件下，DNDS对磷酸盐外流的抑制率为82 - 87%。似乎红细胞阴离子转运系统带III（Band III）以与磷酸盐类似的方式接受砷酸盐，并且两种阴离子的一部分通量可能通过带III以外的途径发生。因此，在人类红细胞中，钠泵和阴离子交换转运系统都会接受砷酸盐作为磷酸盐类似物，并且蛋白质 - 砷酸盐相互作用与蛋白质 - 磷酸盐相互作用非常相似。
