Microcrystals of photosystem II (PSII) have recently been used to investigate the intermediate structures of the water oxidizing complex during water oxidation by serial femtosecond crystallography using X-ray free electron lasers. To clarify the water oxidation mechanism, it is crucial to know whether the reaction proceeds properly in the microcrystals. In this work, we monitored the water oxidation reaction in a single PSII microcrystal using Fourier transform infrared (FTIR) microspectroscopy with the transmission method. Flash-induced micro-FTIR difference spectra of S-state transitions in a PSII microcrystal showed features virtually identical to the corresponding spectra previously obtained using the attenuated total reflection method for multiple microcrystals, representing the reactions near the crystal surface, as well as the spectra in solution. This observation indicates that the reaction processes of water oxidation proceed with relatively high efficiencies retaining native intermediate structures in the entire inside of a PSII microcrystal.

中文翻译：

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在单光系统II微晶中水氧化反应的FTIR显微分析。

最近使用光系统II（PSII）的微晶通过使用X射线自由电子激光的连续飞秒晶体学研究了水氧化过程中水氧化配合物的中间结构。为了阐明水的氧化机理，至关重要的是要知道反应是否在微晶中正确进行。在这项工作中，我们使用透射法通过傅里叶变换红外（FTIR）显微技术监测单个PSII微晶中的水氧化反应。闪光诱导的PSII微晶中S态跃迁的微FTIR差异光谱显示的特征与先前使用衰减全反射法对多个微晶获得的对应光谱几乎相同，表示晶体表面附近的反应，以及溶液中的光谱。该观察结果表明水氧化的反应过程以相对较高的效率进行，从而在PSII微晶的整个内部保留了天然的中间结构。