ORIENTATION OF THE OXYGEN-EVOLVING MANGANESE COMPLEX IN A PHOTOSYSTEM-II MEMBRANE PREPARATION - AN X-RAY-ABSORPTION SPECTROSCOPY STUDY
ORIENTATION OF THE OXYGEN-EVOLVING MANGANESE COMPLEX IN A PHOTOSYSTEM-II MEMBRANE PREPARATION - AN X-RAY-ABSORPTION SPECTROSCOPY STUDY
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DOI：
10.1021/bi00198a042
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发表时间：
1994-08-16
期刊：
影响因子：
2.9
通讯作者：
KLEIN, MP
中科院分区：
文献类型：
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作者：
MUKERJI, I;ANDREWS, JC;KLEIN, MP
X射线吸收光谱已进行定向光系统II膜颗粒分离菠菜。四核锰簇的结构特征和相对于脂质双层的簇的取向被确定在两个S-1和S-2状态的Kok循环。相对于X-射线e-向量的样品取向的变化产生高度二向色性K-边和扩展的X-射线吸收精细结构光谱（EXAFS），指示不对称的四核簇。在2.72和3.38埃处的Mn-Mn矢量可以使用定量分析从这些测量中解析。由至少两个分量矢量组成的2.72埃矢量以与膜法线成60度+/-7度的平均角度取向，每个Mn原子平均具有1.1 +/-0.1相互作用。3.38埃矢量，最可能是两个矢量的平均值，相对于膜法线形成43度+/-10度的角度，每个Mn原子平均有0.45 +/-0.07个反向散射体。在推进到S-2状态时，这些矢量的取向和后向散射体的平均数量近似不变。EXAFS的更微妙的功能分析揭示了伴随着这一S-状态的进步，是一致的氧化锰在此过渡期间的变化。然而，在S-1和S-2状态下，放氧复合物的主要结构特征保持不变。在X射线吸收数据的二色性背景下讨论了锰配合物的结构和配合物在膜中的取向。
X-ray absorption spectroscopy has been performed on oriented photosystem II membrane particles isolated from spinach. Structural features of the tetranuclear Mn cluster and the orientation of the cluster with respect to the lipid bilayer were determined in both the S-1 and S-2 states of the Kok cycle. Variation of the sample orientation with respect to the X-ray e-vector yields highly dichroic K-edge and extended X-ray absorption fine structure spectra (EXAFS), indicative of an asymmetric tetranuclear cluster. Mn-Mn vectors at 2.72 and 3.38 Angstrom can be resolved from these measurements using quantitative analysis. The 2.72-Angstrom vector, consisting of at least two component vectors, is oriented at an average angle of 60 degrees +/- 7 degrees to the membrane normal, with an average of 1.1 +/- 0.1 interactions per Mn atom. The 3.38-Angstrom vector, most probably an average of two vectors, makes an angle of 43 degrees +/- 10 degrees with respect to the membrane normal, with an average of 0.45 +/- 0.07 backscatterer per Mn atom. Upon advance to the S-2 state, the orientation of these vectors and the average numbers of backscatterers are approximately invariant. Analysis of more subtle features of the EXAFS reveals changes accompanying this S-state advance that are consistent with the oxidation of Mn during this transition. However, the dominant structural features of the oxygen-evolving complex remain constant in the S-1 and S-2 states. The structure of the Mn complex and the orientation of the complex in the membrane within the context of dichroism of the X-ray absorption data are discussed.