Eisenberger P, Okamura M Y, Feher G
Biophys J. 1982 Feb;37(2):523-38. doi: 10.1016/S0006-3495(82)84698-5.
Extended x-ray absorption fine structure (EXAFS) studies were performed on reaction centers (RC) of the photosynthetic bacterium Rhodopseudomonas sphaeroides R-26. RC containing two, one, and no quinones (2Q, 1Q, 0Q) samples were studied. The average ligand distance of the first coordination shell was determined to be 2.10 +/- 0.02 A with a more distant shell at 4.14 +/- 0.05 A. The Fe2+ site in RC was found to have a very large structural disorder parameter, from which a spread in ligand distance per iron site of approximately +/- 0.1 A was deduced. The most likely coordination number of the first shell is six, with a mixture of oxygens and nitrogens as ligands. The edge absorption results are consistent with the Fe2+ being in distorted octahedral environment. The EXAFS spectra of the 2Q and 1Q samples with and without O-phenanthroline were found to be the same. This indicates that either the secondary quinone and o-phenanthroline do not bind to Fe2+ or that they replace an equivalent ligand. The 0Q sample showed a 12% decrease in the EXAFS amplitude, which was restored upon addition of o-phenanthroline. These results can be explained by either a loss of a ligand or a severe conformational change when the primary quinone was removed.
对光合细菌球形红假单胞菌R-26的反应中心（RC）进行了扩展X射线吸收精细结构（EXAFS）研究。研究了含有两个醌、一个醌和不含醌（2Q、1Q、0Q）的RC样品。确定第一配位层的平均配体距离为2.10±0.02 Å，更远的一层为4.14±0.05 Å。发现RC中的Fe2+位点具有非常大的结构无序参数，由此推断每个铁位点的配体距离分布约为±0.1 Å。第一层最可能的配位数为6，配体为氧和氮的混合物。边缘吸收结果与Fe2+处于扭曲的八面体环境一致。发现有和没有邻菲罗啉的2Q和1Q样品的EXAFS光谱相同。这表明要么次级醌和邻菲罗啉不与Fe2+结合，要么它们取代了等效的配体。0Q样品的EXAFS振幅降低了12%，加入邻菲罗啉后恢复。这些结果可以通过去除初级醌时配体的损失或严重的构象变化来解释。
