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首页> 美国卫生研究院文献>Proceedings of the National Academy of Sciences of the United States of America >PNAS Plus: Structural rearrangements preceding dioxygen formation by the water oxidation complex of photosystem II
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PNAS Plus: Structural rearrangements preceding dioxygen formation by the water oxidation complex of photosystem II

机译：PNAS Plus：光系统II的水氧化络合物形成双氧之前的结构重排

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摘要

Photosynthetic water oxidation is catalyzed by the Mn4CaO5 cluster of photosystem II. Recent studies implicate an oxo bridge atom, O5, of the Mn4CaO5 cluster, as the “slowly exchanging” substrate water molecule. The D1-V185N mutant is in close vicinity of O5 and known to extend the lag phase and retard the O2 release phase (slow phase) in this critical last S3+→S0 transition of water oxidation. The pH dependence, hydrogen/deuterium (H/D) isotope effect, and temperature dependence on the O2 release kinetics for this mutant were studied using time-resolved O2 polarography, and comparisons were made with WT and two mutants of the putative proton gate D1-D61. Both kinetic phases in V185N are independent of pH and buffer concentration and have weaker H/D kinetic isotope effects. Each phase is characterized by a parallel or even lower activation enthalpy but a less favorable activation entropy than the WT. The results indicate new rate-determining steps for both phases. It is concluded that the lag does not represent inhibition of proton release but rather, slowing of a previously unrecognized kinetic phase involving a structural rearrangement or tautomerism of the S3+ ground state as it approaches a configuration conducive to dioxygen formation. The parallel impacts on both the lag and O2 formation phases suggest a common origin for the defects surmised to be perturbations of the H-bond network and the water cluster adjacent to O5.
机译：光合作用II的Mn4CaO5团簇催化光合水的氧化。最近的研究表明，Mn4CaO5团簇的氧桥原子O5是“缓慢交换”的底物水分子。 D1-V185N突变体在O5的附近，并且已知在这个关键的最后 S 3 + → S 0 过渡。使用时间分辨O2极谱法研究了该突变体的pH依赖性，氢/氘（H / D）同位素效应和温度对O2释放动力学的依赖性，并与WT和推定的质子门D1的两个突变体进行了比较。 -D61。 V185N中的两个动力学相均与pH和缓冲液浓度无关，并且具有较弱的H / D动力学同位素效应。每个阶段的特征在于平行的或什至更低的活化焓，但是活化熵比WT低。结果表明了两个阶段的新的速率确定步骤。结论是，滞后并不代表抑制质子释放，而是减慢了先前无法识别的动力学期，该动力学期涉及结构态重排或S3 + 基态的互变异构，因为它接近于有助于双氧的构型。编队。对滞后和O2形成阶段的平行影响表明，缺陷的共同起因据推测是H键网络和O5附近的水团簇的扰动。

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