Loiseau A, Hill M, Mulliert G, Castaing M
U-251 INSERM, Faculté de Médecine Xavier-Bichat, Paris, France.
Biochim Biophys Acta. 1995 Apr 12;1235(1):21-32. doi: 10.1016/0005-2736(94)00269-u.
The kinetics of the competitive transport of Na+ and K+ ions across the membrane of large unilamellar vesicles (LUV) were determined when transport was induced by (221)C10-cryptand, an ionizable mobile carrier. The experiments were performed at various pH values (7.7 and 8.7) and carrier concentrations (0.1, 0.5 and 1.0 microM) in order to quantify the effects of these parameters on the Na/K competitive transport selectivity of this mobile carrier. At any given pH and carrier concentration, the apparent affinity of (221)C10 for Na+ was higher and less dependent on the concentration of the other competing ion than that for K+. The Na/K competitive transport selectivity (SC(Na/K)) of (221)C10 increased linearly with the Na+ concentrations, decreased hyperbolically with increasing those of K+ and was independent of the pH and of the carrier concentration. In equimolecular ionic mixtures, this competitive selectivity amounted to about 1.5 and when the pH rose, the carrier selectivity for Na+ over K+ ions was enhanced by cation competition compared to transport of cations as unique substrates. Equations were established to describe the variations of the competitive transport selectivity (SC) of cryptands, and for comparison of their noncompetitive selectivity (SNC), with the ionic concentrations, the Michaelis parameters of the cations and the pH. The reaction order in Na+ (n(Na)) increased significantly with decreasing the pH and the K+ concentration. The results are discussed in terms of the structural, physico-chemical and electrical characteristics of carriers and complexes.
当由可电离的移动载体（221）C10 - 穴醚诱导运输时，测定了Na⁺和K⁺离子跨大单层囊泡（LUV）膜的竞争性运输动力学。实验在不同的pH值（7.7和8.7）和载体浓度（0.1、0.5和1.0微摩尔）下进行，以量化这些参数对该移动载体的Na/K竞争性运输选择性的影响。在任何给定的pH值和载体浓度下，（221）C10对Na⁺的表观亲和力更高，并且比其对K⁺的亲和力更少依赖于其他竞争离子的浓度。（221）C10的Na/K竞争性运输选择性（SC(Na/K)）随Na⁺浓度线性增加，随K⁺浓度增加呈双曲线下降，并且与pH值和载体浓度无关。在等分子离子混合物中，这种竞争性选择性约为1.5，并且当pH升高时，与阳离子作为唯一底物的运输相比，阳离子竞争增强了载体对Na⁺相对于K⁺离子的选择性。建立了方程来描述穴醚竞争性运输选择性（SC）的变化，以及用于比较它们的非竞争性选择性（SNC）与离子浓度、阳离子的米氏参数和pH值之间的关系。Na⁺的反应级数（n(Na)）随着pH值和K⁺浓度的降低而显著增加。根据载体和配合物的结构、物理化学和电学特性对结果进行了讨论。
