Kusunoki M, Ono T, Matsushita T, Oyanagi H, Inoue Y
School of Science and Technology, Meiji University, Kanagawa.
J Biochem. 1990 Oct;108(4):560-7. doi: 10.1093/oxfordjournals.jbchem.a123242.
High-resolution XANES (X-ray Absorption Near Edge Structure) spectroscopy for Mn in the S1 and S2 states of the spinach photosynthetic O2-evolving complex revealed distinct features in K-edge spectra, when a high signal-to-noise (S/N) ratio of ca. 80 with a low and constant background-to-signal (B/S) ratio of 0.15 to 0.18 was attained. Six features resolved in each S-state spectrum involve a pre-edge feature due to 1s----3d transitions, a main-edge feature possibly due to 1s----4s transitions and four fine structures superimposed on the principal absorption bands due to 1s----4p* transitions. The high-quality pre-edge features were analyzed according to a parametric ligand-field theory in comparison with those of some typical authentic Mn complexes. It was deduced that i) all of the four Mn ions in the S1-state are octahedrally coordinated and two of them constitute a di-mu-oxo bridged Mn(III, III) dimeric subunit; ii) the bridged Mn(III) ions are further bridged by a deprotonated water dimer, (HOHOH)-, and coordinated by imidazole-N and carboxylate-O- on the opposite side of the Mn atom from the di-mu-oxo bridge; iii) the other two Mn ions exist in the form of Mn(III) monomeric subunits; and iv) upon the S1----S2 transition, only the bridged Mn(III,III) is oxidized to Mn(III,IV). The distinct change in the principal absorption band shape upon the S1----S2 transition is briefly discussed to obtain the XANES evidence for a tetrameric Mn-cluster.
对菠菜光合放氧复合体S1和S2状态下的锰进行高分辨率X射线吸收近边结构（XANES）光谱分析时，当达到约80的高信噪比（S/N）以及0.15至0.18的低且恒定的背景信号比（B/S）时，K边光谱显示出明显特征。每个S态光谱中分辨出的六个特征包括：由于1s→3d跃迁产生的预边特征、可能由于1s→4s跃迁产生的主边特征以及由于1s→4p*跃迁叠加在主吸收带上的四个精细结构。根据参数配体场理论，将高质量的预边特征与一些典型的真实锰配合物的特征进行了比较分析。推断出：i）S1态中的所有四个锰离子均为八面体配位，其中两个构成双μ-氧桥联的Mn(III, III)二聚体亚基；ii）桥联的Mn(III)离子进一步由去质子化的水二聚体(HOHOH)-桥联，并在与双μ-氧桥相对的锰原子一侧由咪唑-N和羧酸盐-O配位；iii）另外两个锰离子以Mn(III)单体亚基的形式存在；iv）在S1→S2转变过程中，只有桥联的Mn(III,III)被氧化为Mn(III,IV)。简要讨论了S1→S2转变时主吸收带形状的明显变化，以获得关于四聚体锰簇的XANES证据。
