FTIR detection of water reactions during the flash-induced S-state cycle of the photosynthetic water-oxidizing complex
FTIR detection of water reactions during the flash-induced S-state cycle of the photosynthetic water-oxidizing complex
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DOI：
10.1021/bi020603i
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发表时间：
2002-12-31
期刊：
影响因子：
2.9
通讯作者：
Sugiura, M
中科院分区：
文献类型：
--
作者：
Noguchi, T;Sugiura, M
光合水氧化是通过光系统II（PS II）的水氧化复合物（WOC）中的光驱动S态循环进行的。为了理解其分子机制，监测每个S态转变中的底物水反应是必不可少的。我们已经首次检测到的反应，在WOC的水分子在整个S-状态循环通过观察OH振动的水，使用闪光诱导傅里叶变换红外（FTIR）差光谱。以细长聚球藻（Synechococcuselongatus）的PS Ⅱ核心膜为研究对象，分别在第一、第二、第三和第四次闪光照射下，获得了表征S-1 --> S-2、S-2 --> S-3、S-3 --> S-0和S-0 --> S-1跃迁的FTIR差谱。在弱氢键OH区域，在第一次闪光光谱中，3617/3588 cm（-1）处出现了差分信号带，在第二次、第三次和第四次闪光光谱中，分别在3634、3621和3612 cm（-1）处出现了负强度带。这些谱带在氘代时下移约940 cm（-1），在（HO）-O-18取代时下移约10 cm（-1），表明它们来自水的OH伸展，包括底物及其中间体。通过对氘代膜（D_2O）-O ~（16）-和氘代膜（D_2O）-O ~（18）-的光谱进行双差分析，确定了水分子在2600-2200 cm ~（-1）范围内的强D键OD带。此外，在水合PS II膜的第一、第二、第三和第四次闪光光谱中，分别在3000、2700、2550和2600 cm（-1）附近观察到可能由氢键的大质子极化率引起的宽连续谱特征，揭示了蛋白质氢键网络的变化。第二至第四次闪光时的负OH强度可能与基质水的质子释放有关。研究结果表明，利用红外光谱检测水OH（D）谱带是研究光合水氧化机理的有效方法。
Photosynthetic water oxidation is performed via the light-driven S-state cycle in the water-oxidizing complex (WOC) of photosystem II (PS II). To understand its molecular mechanism, monitoring the reaction of substrate water in each S-state transition is essential. We have for the first time detected the reactions of water molecules in WOC throughout the S-state cycle by observing the OH vibrations of water using flash-induced Fourier transform infrared (FTIR) difference spectroscopy. Moderately hydrated (or deuterated) PS II core films from Synechococcus elongatus were used to obtain the FTIR difference spectra upon the first, second, third, and fourth flash illumination, representing the structural changes in the S-1 --> S-2, S-2 --> S-3, S-3 --> S-0, and S-0 --> S-1 transitions, respectively. In the weakly H-bonded OH region, bands appeared at 3617/3588 cm(-1) as a differential signal in the first-flash spectrum and at 3634, 3621, and 3612 cm(-1) with negative intensities in the second-, third-, and fourth-flash spectra, respectively. These bands shifted down by similar to940 cm(-1) upon deuteration and by similar to10 cm(-1) upon (HO)-O-18 substitution, indicating that they arise from the OH stretches of water including the substrate and its intermediates. Stronuly D-bonded OD bands of water were also identified as broad features in the range of 2600-2200 cm(-1) by taking the double difference between the spectra of (D2O)-O-16- and (D2O)-O-18-deuterated films. In addition, broad continuum features that probably arise from the large proton polarizability of H-bonds were observed around 3000, 2700, 2550, and 2600 cm(-1) in the first-, second-, third-, and fourth-flash spectra, respectively, of the hydrated PS II film, revealing changes in the H-bond network of the protein. The negative OH intensities upon the second to fourth flashes might be related to proton release from substrate water. The results presented here showed that FTIR detection of water OH(D) bands can be a powerful method for investigating the mechanism of photosynthetic water oxidation.