Della Longa S, Pin S, Cortès R, Soldatov A V, Alpert B
Dept. Medicina Sperimentale and INFM, Università dell'Aquila, I-67100 L'Aquila and Ist. Naz. Fisica Materia (INFM), Italy. dellalongo@vaxaq
Biophys J. 1998 Dec;75(6):3154-62. doi: 10.1016/S0006-3495(98)77757-4.
X-ray absorption near-edge structure (XANES) spectra of ferric myoglobin from horse heart have been acquired as a function of pH (between 5.3 and 11.3). At pH = 11.3 temperature-dependent spectra (between 20 and 293 K) have been collected as well. Experimental data solve three main conformations of the Fe-heme: the first, at low pH, is related to high-spin aquomet-myoglobin (Mb+OH2). The other two, at pH 11.3, are related to hydroxymet-myoglobin (Mb+OH-), and are in thermal equilibrium, corresponding to high- and low-spin Mb+OH-. The structure of the three Fe-heme conformations has been assigned according to spin-resolved multiple scattering simulations and fitting of the XANES data. The chemical transition between Mb+OH2 and high-spin Mb+OH-, and the spin transition of Mb+OH-, are accompanied by changes of the Fe coordination sphere due to its movement toward the heme plane, coupled to an increase of the axial asymmetry.
已获取马心肌红蛋白的X射线吸收近边结构（XANES）光谱，该光谱是pH值（5.3至11.3之间）的函数。在pH = 11.3时，还收集了温度相关光谱（20至293 K之间）。实验数据解析了铁-血红素的三种主要构象：第一种，在低pH值下，与高自旋水合肌红蛋白（Mb + OH2）有关。另外两种，在pH 11.3时，与羟基肌红蛋白（Mb + OH-）有关，并且处于热平衡状态，分别对应于高自旋和低自旋的Mb + OH-。根据自旋分辨多重散射模拟和XANES数据拟合，确定了三种铁-血红素构象的结构。Mb + OH2与高自旋Mb + OH-之间的化学转变以及Mb + OH-的自旋转变，伴随着铁配位球的变化，这是由于其向血红素平面移动，并伴随着轴向不对称性的增加。
