Russu I M, Wu S S, Ho N T, Kellogg G W, Ho C
Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213.
Biochemistry. 1989 Jun 13;28(12):5298-306. doi: 10.1021/bi00438a057.
High-resolution proton nuclear magnetic resonance spectroscopy has been used to investigate the molecular mechanism of the Bohr effect of human normal adult hemoglobin in the presence of two allosteric effectors, i.e., chloride and inorganic phosphate ions. The individual hydrogen ion equilibria of 22-26 histidyl residues of hemoglobin have been measured in anion-free 0.1 M HEPES buffer and in the presence of 0.18 M chloride or 0.1 M inorganic phosphate ions in both deoxy and carbonmonoxy forms. The results indicate that the beta 2-histidyl residues are strong binding sites for chloride and inorganic phosphate ions in hemoglobin. The affinity of the beta 2-histidyl residues for these anions is larger in the deoxy than in the carbonmonoxy form. Nevertheless, the contribution of these histidyl residues to the anion Bohr effect is small due to their low pK value in deoxyhemoglobin in anion-free solvents. The interactions of chloride and inorganic phosphate ions with the hemoglobin molecule also result in lower pK values and/or changes in the shapes of the hydrogen ion binding curves for several other surface histidyl residues. These results suggest that long-range electrostatic interactions between individual ionizable sites in hemoglobin could play an important role in the molecular mechanism of the anion Bohr effect.
高分辨率质子核磁共振光谱已被用于研究在两种变构效应剂（即氯离子和无机磷酸根离子）存在下，成人正常血红蛋白玻尔效应的分子机制。在无阴离子的0.1 M HEPES缓冲液中，以及在脱氧和碳氧血红蛋白形式下分别存在0.18 M氯离子或0.1 M无机磷酸根离子的情况下，测量了血红蛋白22 - 26个组氨酸残基的单个氢离子平衡。结果表明，β2 - 组氨酸残基是血红蛋白中氯离子和无机磷酸根离子的强结合位点。β2 - 组氨酸残基对这些阴离子的亲和力在脱氧形式中比在碳氧血红蛋白形式中更大。然而，由于它们在无阴离子溶剂中的脱氧血红蛋白中pK值较低，这些组氨酸残基对阴离子玻尔效应的贡献较小。氯离子和无机磷酸根离子与血红蛋白分子的相互作用还导致其他几个表面组氨酸残基的pK值降低和/或氢离子结合曲线形状的变化。这些结果表明，血红蛋白中各个可电离位点之间的长程静电相互作用可能在阴离子玻尔效应的分子机制中起重要作用。
