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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Photosynthetic Water Oxidation At Elevated Dioxygen Partial Pressure Monitored By Time-resolved X-ray Absorption Measurements
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Photosynthetic Water Oxidation At Elevated Dioxygen Partial Pressure Monitored By Time-resolved X-ray Absorption Measurements

机译：通过时间分辨的X射线吸收测量监测双氧分压升高下的光合水氧化

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摘要

The atmospheric dioxygen (O_2) is produced at a tetramanganese complex bound to the proteins of photosystem II (PSII). To investigate product inhibition at elevated oxygen partial pressure (pO_2 ranging from 0.2 to 16 bar), we monitored specifically the redox reactions of the Mn complex in its catalytic S-state cycle by rapid-scan and time-resolved X-ray absorption near-edge spectros-copy (XANES) at the Mn K-edge. By using a pressure cell for X-ray measurements after laser-flash excitation of PSII particles, we found a clear pO_2 influence on the redox reactions of the Mn complex, with a similar half-effect pressure as determined (2-3 bar). However, XANES spectra and the time courses of the X-ray fluorescence collected with microsecond resolution suggested that the O_2 evolution transition itself (S_3→S_0+O_2) was not affected. Additional (nonstandard) oxidation of the Mn complex at high pO_2 explains our experimental findings more readily. Our results suggest that photosynthesis at ambient conditions is not limited by product inhibition of the O_2 formation step.
机译：在与光系统II（PSII）的蛋白质结合的四锰配合物中产生了大气中的双氧（O_2）。为了研究在较高的氧分压下（pO_2在0.2至16 bar之间）的产物抑制作用，我们通过快速扫描和时间分辨的X射线吸收法，专门监测了锰配合物在其催化S状态循环中的氧化还原反应。 Mn K边缘的边缘光谱（XANES）。通过在PSII粒子的激光闪光激发后使用压力传感器进行X射线测量，我们发现pO_2对Mn络合物的氧化还原反应有明显的影响，确定的半效应压力类似（2-3 bar）。然而，XANES光谱和以微秒分辨率收集的X射线荧光的时间过程表明，O_2的演化转变本身（S_3→S_0 + O_2）不受影响。高pO_2时锰配合物的其他（非标准）氧化作用更容易说明我们的实验结果。我们的结果表明，在环境条件下的光合作用不受O_2形成步骤产物抑制的限制。

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