Milanick M A, Gunn R B
Am J Physiol. 1986 Jun;250(6 Pt 1):C955-69. doi: 10.1152/ajpcell.1986.250.6.C955.
The inhibition of chloride exchange at 0 degrees C by protons at the cytoplasmic and the extracellular surface of the band 3 protein of human erythrocytes was measured between pH 4.6 and 7.6. At constant external pH and chloride concentration, internal protons were a mixed inhibitor of chloride flux, with the apparent pK2 = 6.1 for protonation of the inward-facing empty transporter conformation and the apparent pK3 = 5.7 for protonation of the chloride-transporter complex. The activation of chloride exchange by external chloride was inhibited by internal protons, and internal protonation of the externally facing empty conformation had a pK1 = 6.1. External protons were also a mixed inhibitor of chloride exchange with the apparent pK1 = 5.0 for the empty outward-facing transporter conformation. Because of the pHo dependence of self-inhibition, the value of pK3 on the outside for chloride could not be accurately determined, but the apparent pK3 for protonation of the iodide-transporter complex on the extracellular surface was 4.9. The data support a mechanism with a single proton binding site that can alternatively have access to the cytoplasmic and extracellular solutions. It appears that this proton binding and transport site can be coupled to the single anion transport site for cotransport, but the two sites can be on opposite sides of the membrane at the same time and thus can be asynchronously transported by conformational changes of band 3.
在pH值4.6至7.6之间，测定了0℃时人红细胞带3蛋白细胞质和细胞外表面质子对氯离子交换的抑制作用。在外部pH值和氯离子浓度恒定的情况下，内部质子是氯离子通量的混合抑制剂，向内空转运体构象质子化的表观pK2 = 6.1，氯离子 - 转运体复合物质子化的表观pK3 = 5.7。外部氯离子对氯离子交换的激活作用受到内部质子的抑制，向外空构象的内部质子化的pK1 = 6.1。外部质子也是氯离子交换的混合抑制剂，向外空转运体构象的表观pK1 = 5.0。由于自我抑制对细胞外pH值的依赖性，无法准确测定外部氯离子的pK3值，但细胞外表面碘离子 - 转运体复合物质子化的表观pK3为4.9。这些数据支持一种具有单个质子结合位点的机制，该位点可以交替地接触细胞质和细胞外溶液。看来这个质子结合和转运位点可以与单个阴离子转运位点偶联进行共转运，但这两个位点可以同时位于膜的两侧，因此可以通过带3的构象变化进行异步转运。
