Matsuoka A, Kobayashi N, Shikama K
Biological Institute and Pharmaceutical Institute, Tohoku University, Sendai, Japan.
Eur J Biochem. 1992 Nov 15;210(1):337-41. doi: 10.1111/j.1432-1033.1992.tb17426.x.
To find a simple criterion for the presence of the distal (E7) histidine residue in myoglobins and hemoglobins, the Soret magnetic-circular-dichroic spectra were examined for ferric metmyoglobins from various species. A distinct and symmetric dispersion-type curve was obtained for myoglobins containing the distal histidine, whereas a relatively weak and unsymmetric pattern was observed for myoglobins lacking this residue, such as those from three kinds of gastropodic sea molluscs, a shark and the African elephant. The magnetic-circular-dichroic spectra obtained would thus be a direct reflection of the presence or absence of a water molecule at the sixth coordinate position of the heme iron(III), this axial water ligand being stabilized by hydrogen-bond formation to the distal histidine residue. On the basis of these Soret magnetic-circular-dichroic signals, we also examined the structure of a protozoan myoglobin (or a monomeric hemoglobin) from Paramecium caudatum of particular interest for the evolution of these proteins from protozoa to higher animals.
为了找到肌红蛋白和血红蛋白中远端（E7）组氨酸残基存在的简单标准，我们研究了来自不同物种的高铁肌红蛋白的Soret磁圆二色光谱。对于含有远端组氨酸的肌红蛋白，获得了明显且对称的色散型曲线，而对于缺乏该残基的肌红蛋白，如来自三种腹足纲海洋软体动物、鲨鱼和非洲象的肌红蛋白，则观察到相对较弱且不对称的模式。因此，所获得的磁圆二色光谱将直接反映血红素铁（III）第六配位位置上水分子的存在与否，这种轴向水配体通过与远端组氨酸残基形成氢键而得以稳定。基于这些Soret磁圆二色信号，我们还研究了来自尾草履虫的原生动物肌红蛋白（或单体血红蛋白）的结构，该蛋白对于这些蛋白质从原生动物到高等动物的进化具有特别的意义。
