Koshikawa K, Yamamoto Y, Kamimura S, Matsuoka A, Shikama K
Department of Chemistry, University of Tsukuba, Tsukuba 305-8571, Japan.
Biochim Biophys Acta. 1998 Jun 11;1385(1):89-100. doi: 10.1016/s0167-4838(98)00051-x.
One of the components of hemoglobin from the larval hemolyph of Tokunagayusurika akamusi possesses naturally occurring substitution at the E7 helical position (Leu E7) [M. Fukuda, T. Takagi, K. Shikama, Biochim. Biophys. Acta 1157 (1993) 185-191]. Its oxygen affinity is almost comparable to those of mammalian myoglobins and it exhibits Bohr effect. Both acidic and alkaline forms of the ferric hemoglobin have been investigated using 1H NMR in order to gain insight into molecular mechanisms for relatively high oxygen affinity and Bohr effect of this protein. The NMR data indicated that the acidic form of the protein possesses pentacoordinated heme, and that the alkaline form possessing OH- appears with increasing the pH value. pH titration yielded a pK value of 7.2 for the acid-alkaline transition, and this value is the lowest among the values reported so far for various myoglobins and hemoglobins. The kinetic measurements of the transition revealed that the activation energy for the dissociation of the Fe-bound OH-, as well as the dissociation and association rates, decrease with increasing the pH value. These pH dependence properties are likely to be related to the Bohr effect of this protein.
来自赤拟谷盗幼虫血淋巴的血红蛋白的一个组分在E7螺旋位置（亮氨酸E7）存在天然取代 [深田M，高木T，鹿间K，《生物化学与生物物理学学报》1157 (1993) 185 - 191]。其氧亲和力几乎与哺乳动物肌红蛋白相当，并且表现出波尔效应。为了深入了解该蛋白质相对较高的氧亲和力和波尔效应的分子机制，使用1H NMR对高铁血红蛋白的酸性和碱性形式都进行了研究。NMR数据表明，该蛋白质的酸性形式具有五配位血红素，并且随着pH值升高出现含有OH-的碱性形式。pH滴定得到酸 - 碱转变的pK值为7.2，该值是迄今为止报道的各种肌红蛋白和血红蛋白的值中最低的。转变的动力学测量表明，Fe结合的OH-解离的活化能以及解离和缔合速率都随着pH值升高而降低。这些pH依赖性特性可能与该蛋白质的波尔效应有关。
