Kern Jan, Renger Gernot
Institut für Chemie, Max-Volmer-Laboratorium für Biophysikalische Chemie, Technische Universität Berlin, Strasse des 17. Juni 135, 10623, Berlin, Germany.
Photosynth Res. 2007 Nov-Dec;94(2-3):183-202. doi: 10.1007/s11120-007-9201-1. Epub 2007 Jul 17.
This mini-review briefly summarizes our current knowledge on the reaction pattern of light-driven water splitting and the structure of Photosystem II that acts as a water:plastoquinone oxidoreductase. The overall process comprises three types of reaction sequences: (a) light-induced charge separation leading to formation of the radical ion pair P680+QA(-) ; (b) reduction of plastoquinone to plastoquinol at the QB site via a two-step reaction sequence with QA(-) as reductant and (c) oxidative water splitting into O2 and four protons at a manganese-containing catalytic site via a four-step sequence driven by P680+ as oxidant and a redox active tyrosine YZ acting as mediator. Based on recent progress in X-ray diffraction crystallographic structure analysis the array of the cofactors within the protein matrix is discussed in relation to the functional pattern. Special emphasis is paid on the structure of the catalytic sites of PQH2 formation (QB-site) and oxidative water splitting (Mn4OxCa cluster). The energetics and kinetics of the reactions taking place at these sites are presented only in a very concise manner with reference to recent up-to-date reviews. It is illustrated that several questions on the mechanism of oxidative water splitting and the structure of the catalytic sites are far from being satisfactorily answered.
本综述简要总结了我们目前对光驱动水分解反应模式以及作为水-质体醌氧化还原酶的光系统II结构的认识。整个过程包括三种反应序列：(a) 光诱导电荷分离导致形成自由基离子对P680+QA(-)；(b) 在QB位点通过以QA(-*)为还原剂的两步反应序列将质体醌还原为质体醌醇；(c) 在含锰催化位点通过由P680+*作为氧化剂和氧化还原活性酪氨酸YZ作为介质驱动的四步序列将水氧化分解为O2和四个质子。基于X射线衍射晶体结构分析的最新进展，讨论了蛋白质基质中辅因子的排列与功能模式的关系。特别强调了PQH2形成的催化位点（QB位点）和水氧化分解的催化位点（Mn4OxCa簇）结构。参考最近的最新综述，仅以非常简洁的方式介绍了在这些位点发生的反应的能量学和动力学。结果表明，关于水氧化分解机制和催化位点结构的几个问题远未得到令人满意的解答。
