Water Oxidation by Photosystem II: H2O-D2O Exchange and the Influence of pH Support Formation of an Intermediate by Removal of a Proton before Dioxygen Creation
Water Oxidation by Photosystem II: H2O-D2O Exchange and the Influence of pH Support Formation of an Intermediate by Removal of a Proton before Dioxygen Creation
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DOI：
10.1021/bi101198n
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发表时间：
2010-11-30
期刊：
影响因子：
2.9
通讯作者：
Dau, Holger
中科院分区：
文献类型：
--
作者：
Gerencser, Laszlo;Dau, Holger
了解光合水氧化的化学需要更深入地了解电子转移（ET）和质子迁移之间的相互关系。在光系统II膜颗粒中，水-氧化性Mn络合物的氧化还原转变由纳秒激光闪光引发，并通过360 nm处的吸收光谱（A（360））监测。在析氧转变（S-3 + hv -> S-0 + O-2）中，A（360）的指数下降（τ（O2），= 1.6 ms）可归因于Mn还原和O-2形成。相应的速率决定步骤是从Mn络合物到酪氨酸自由基的ET（Y-Z（OX））。我们发现，这种A（360）减少之前的滞后期与持续时间为170 +/- 40 μ s（tau（滞后）在pH 6.2），表明形成的中间体之前ET和O-O键形成和证实的结果，通过时间分辨X-射线光谱。尽管tau（O2）表现出较小的动力学同位素效应和可忽略的pH依赖性，但在D2 O（tau（滞后）增加类似于D2 O中的140%）和低pH（在pH 7.0时tau（滞后）为30 +/- 20 μ s，而在pH 5.5时tau（滞后）为470 +/- 80 μ s）下，中间体的形成均显著减慢。这些研究结果支持了这样的事实，即在析氧过渡的中间体是通过去质子化和去除质子从锰复合物，Y-Z（OX）形成后，但在电子转移和O-O键形成的发病。
Understanding the chemistry of photosynthetic water oxidation requires deeper insight into the interrelation between electron transfer (ET) and proton relocations. In photosystem II membrane particles, the redox transitions of the water-oxidizing Mn complex were initiated by nanosecond laser flashes and monitored by absorption spectroscopy at 360 nm (A(360)). In the oxygen evolution transition (S-3 + hv -> S-0 + O-2), an exponential decrease in A(360) (tau(O2), = 1.6 ms) can be assigned to Mn reduction and O-2 formation. The corresponding rate-determining step is the ET from the Mn complex to a tyrosine radical (Y-Z(OX)). We find that this A(360) decrease is preceded by a lag phase with a duration of 170 +/- 40 mu s (tau(lag) at pH 6.2), indicating formation of an intermediate before ET and O-O bond formation and corroborating results obtained by time-resolved X-ray spectroscopy. Whereas tau(O2) exhibits a minor kinetic isotope effect and negligible pH dependence, formation of the intermediate is slowed significantly both in D2O (tau(lag) increase of similar to 140% in D2O) and at low pH (tau(lag) of 30 +/- 20 mu s at pH 7.0 vs tau(lag) of 470 +/- 80 mu s at pH 5.5). These findings support the fact that in the oxygen evolution transition an intermediate is created by deprotonation and removal of a proton from the Mn complex, after Y-Z(OX) formation but before the onset of electron transfer and O-O bond formation.