FTIR detection of water reactions in the oxygen-evolving centre of photosystem II
FTIR detection of water reactions in the oxygen-evolving centre of photosystem II
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DOI：
10.1098/rstb.2007.2214
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发表时间：
2008-03
期刊：
影响因子：
--
通讯作者：
T. Noguchi
中科院分区：
文献类型：
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作者：
T. Noguchi
利用闪光诱导傅里叶变换红外（FTIR）差谱技术研究了光系统II放氧中心的水氧化反应。在S态循环期间，通过检测FTIR差谱中3700-3500 cm−1区域中的水的弱H键合OH的OH伸缩带，直接监测水分子的反应。在S1→S2跃迁中，观察到从3588 cm − 1到3617 cm−1的能带位移，表明氢键减弱。使用D2 O：H2O（1：1）的解耦实验表明，这种OH来自具有不对称氢键结构的水分子，并且这种不对称性在S2形成时变得更加显著。在S2→S3、S3→ S 0和S 0 →S1跃迁中，分别在3634、3621和3612 cm−1处观察到负带，表示形成强氢键或质子释放反应。此外，使用羧酸盐伸缩区域（1600-1300 cm-1）中的复杂光谱特征作为各个S-态转变的“指纹”，检查转变效率和脱水效果的pH依赖性，以获得S-态循环中质子释放和水插入步骤的信息。低pH对S2→S3、S3→ S 0和S 0 →S1跃迁的抑制与质子在S1→S2以外的三个跃迁中释放的观点一致，而在S2→S3和S3→ S 0跃迁中相对较高的脱水敏感性表明在这些跃迁期间基质水插入到系统中。因此，提出了一种可能的水氧化机理来解释FTIR数据。
Flash-induced Fourier transform infrared (FTIR) difference spectroscopy has been used to study the water-oxidizing reactions in the oxygen-evolving centre of photosystem II. Reactions of water molecules were directly monitored by detecting the OH stretching bands of weakly H-bonded OH of water in the 3700–3500 cm−1 region in FTIR difference spectra during S-state cycling. In the S1→S2 transition, a band shift from 3588 to 3617 cm−1 was observed, indicative of a weakened H-bond. Decoupling experiments using D2O : H2O (1 : 1) showed that this OH arose from a water molecule with an asymmetric H-bonding structure and this asymmetry became more significant upon S2 formation. In the S2→S3, S3→S0 and S0→S1 transitions, negative bands were observed at 3634, 3621 and 3612 cm−1, respectively, representing formation of a strong H-bond or a proton release reaction. In addition, using complex spectral features in the carboxylate stretching region (1600–1300 cm−1) as ‘fingerprints’ of individual S-state transitions, pH dependency of the transition efficiencies and the effect of dehydration were examined to obtain the information of proton release and water insertion steps in the S-state cycle. Low-pH inhibition of the S2→S3, S3→S0 and S0→S1 transitions was consistent with a view that protons are released in the three transitions other than S1→S2, while relatively high susceptibility to dehydration in the S2→S3 and S3→S0 transitions suggested the insertion of substrate water into the system during these transitions. Thus, a possible mechanism of water oxidation to explain the FTIR data is proposed.