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首页> 外文期刊>Biochemistry >Proton Release Process during the S-2-to-S-3 Transition of Photosynthetic Water Oxidation As Revealed by the pH Dependence of Kinetics Monitored by Time-Resolved Infrared Spectroscopy
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Proton Release Process during the S-2-to-S-3 Transition of Photosynthetic Water Oxidation As Revealed by the pH Dependence of Kinetics Monitored by Time-Resolved Infrared Spectroscopy

机译：质子释放过程在S-2至S-3的光合水氧化转变期间，通过时间分辨的红外光谱监测的动力学的pH依赖性揭示

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摘要

Photosynthetic water oxidation takes place at the Mn4CaO5 cluster in photosystem II via a light-driven cycle of intermediates called S states (S-0-S-4). Clarifying how electron and proton transfer reactions are coupled with each other in the S-2 -> S-3 transition, which occurs just before O-O bond formation, is crucial for understanding the water oxidation mechanism. Here, we investigated the pH dependence of the kinetics of the S-2 -> S-3 transition using time-resolved infrared (TRIR) spectroscopy to identify the proton release phase in this transition. TRIR measurements of Y-D-less PSII core complexes from the D2-Y160F mutant of Thermosynechococcus elongatus showed that the last phase in this transition (tau similar to 350 mu s at pH 6) was strongly dependent on pH, and its time constant at pH .5 was larger than that at pH 8 by a factor of >3. In contrast, the earlier phase with a time constant of similar to 100 ps was virtually independent of pH. These results strongly support the view that proton release is a rate-limiting step of the proton-coupled electron transfer in the last phase of the S-2 -> S-3 transition. This proton release enables electron transfer by removing an excessive positive charge from the catalytic center and hence decreasing its redox potential.
机译：光合水氧化通过称为S状态的光电循环（S-0-S-4）的光线系统II中的Mn4Cao5集群进行。阐明电子和质子转移反应如何在S-2 - > S-3转变中彼此偶联，该转变在O-O键形成之前发生，对于理解水氧化机理至关重要。在这里，我们研究了使用时间分辨的红外（TRIR）光谱法测定S-2 - > S-3转变的动力学的pH依赖性，以识别该转变中的质子释放相。来自热循环菌的D2-Y160F突变体的YD-DIAI核心复合物的TRIR测量结果表明，该转变中的最后一阶段（在pH 6时类似于350μs）的阶段强烈依赖于pH，并在pH下恒定。 5大于pH8的pH值为3重量倍> 3。相反，具有与100ps类似的时间常数的前相位几乎与pH无关。这些结果强烈支持质子释放是S-2 - > S-3转变的最后阶段的质子耦合电子传输的速率限制步骤。该质子释放通过从催化中心除去过量的正电荷来实现电子传递，从而降低其氧化还原电位。

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  • 来源
    《Biochemistry》 |2019年第42期|共8页
  • 作者

    Takemoto Hiroshi; Sugiura Miwa; Noguchi Takumi;

  • 作者单位

    Nagoya Univ Grad Sch Sci Div Mat Sci Chikusa Ku Furo Cho Nagoya Aichi 4648602 Japan;

    Ehime Univ Proteosci Res Ctr Bunkyo Cho Matsuyama Ehime 7908577 Japan;

    Nagoya Univ Grad Sch Sci Div Mat Sci Chikusa Ku Furo Cho Nagoya Aichi 4648602 Japan;

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  • 正文语种 eng
  • 中图分类 生物化学;
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