Monitoring water reactions during the S-state cycle of the photosynthetic water-oxidizing center: detection of the DOD bending vibrations by means of Fourier transform infrared spectroscopy.
Monitoring water reactions during the S-state cycle of the photosynthetic water-oxidizing center: detection of the DOD bending vibrations by means of Fourier transform infrared spectroscopy.
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DOI：
10.1021/bi801580e
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发表时间：
2008-09
期刊：
影响因子：
2.9
通讯作者：
Hiroyuki Suzuki;M. Sugiura;T. Noguchi
中科院分区：
文献类型：
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作者：
Hiroyuki Suzuki;M. Sugiura;T. Noguchi
光合水氧化作用发生在光系统II（PSII）的水氧化中心（WOC）。为了阐明水氧化的机理，检测WOC中的水分子并在分子水平上监测它们的反应是必不可少的。在这项研究中，我们首次利用傅里叶变换红外（FTIR）差谱技术检测到了WOC S态循环过程中功能D2 O分子的DOD弯曲振动。利用D2（16）O和D2（18）O适度氘代的细长热聚球藻（Thermosynechococcuselongatus）PSII核心复合物，测量了S态跃迁的闪光诱导FTIR差谱。在1250-1150 cm（-1）范围内，D2（16）O减去D2（18）O的双差谱中有6 ~ 8个D（16）OD/D（18）OD弯曲振动峰。这一观察结果表明，至少有两个水分子，而不是在任何去质子化的形式，参与在整个循环中的每个S-状态转换的反应。大多数峰在不同的跃迁处表现出明显的反峰，其符号相反，反映了水分子在催化位点的一系列反应。相反，在S2-> S3、S3-> S 0和可能的S 0 -> S1跃迁中，在大约1240 cm（-1）处的负带，在其他跃迁中没有发现明显的反峰，可以解释为底物水从蛋白质中的水簇插入WOC。弱D键OD伸缩带的特征与S2-> S3和S3-> S 0跃迁中内部水分子插入底物的情况一致。这项研究的结果表明，红外检测的DOD弯曲振动是一个强大的方法，用于调查光合水氧化的分子机制，以及其他酶促反应涉及功能水分子。
Photosynthetic water oxidation takes place in the water-oxidizing center (WOC) of photosystem II (PSII). To clarify the mechanism of water oxidation, detecting water molecules in the WOC and monitoring their reactions at the molecular level are essential. In this study, we have for the first time detected the DOD bending vibrations of functional D 2O molecules during the S-state cycle of the WOC by means of Fourier transform infrared (FTIR) difference spectroscopy. Flash-induced FTIR difference spectra upon S-state transitions were measured using the PSII core complexes from Thermosynechococcus elongatus moderately deuterated with D 2 (16)O and D 2 (18)O. D 2 (16)O-minus-D 2 (18)O double difference spectra at individual S-state transitions exhibited six to eight peaks arising from the D (16)OD/D (18)OD bending vibrations in the 1250-1150 cm (-1) region. This observation indicates that at least two water molecules, not in any deprotonated forms, participate in the reaction at each S-state transition throughout the cycle. Most of the peaks exhibited clear counter peaks with opposite signs at different transitions, reflecting a series of reactions of water molecules at the catalytic site. In contrast, negative bands at approximately 1240 cm (-1) in the S 2 --> S 3, S 3 --> S 0, and possibly S 0 --> S 1 transitions, for which no clear counter peaks were found in other transitions, can be interpreted as insertion of substrate water into the WOC from a water cluster in the proteins. The characteristics of the weakly D-bonded OD stretching bands were consistent with the insertion of substrate from internal water molecules in the S 2 --> S 3 and S 3 --> S 0 transitions. The results of this study show that FTIR detection of the DOD bending vibrations is a powerful method for investigating the molecular mechanism of photosynthetic water oxidation as well as other enzymatic reactions involving functional water molecules.