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首页> 外文期刊>Biochemistry >Vibrational spectrum associated with the reduction of tyrosyl radical D-center dot in photosystem II: A comparative biochemical and kinetic study
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Vibrational spectrum associated with the reduction of tyrosyl radical D-center dot in photosystem II: A comparative biochemical and kinetic study

机译：与光系统​​II中酪氨酰自由基D-中心点减少相关的振动光谱：比较生化和动力学研究

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Photosystem II (PSII) contains a redox-active tyrosine, D. Difference FT-IR spectroscopy can be used to obtain structural information about this species, which is a neutral radical, D-., in the photooxidized form. Previously, we have used isotopic labeling, site-directed mutagenesis, and kinetics to assign a vibrational line at 1477 cm(-1) to D-.; these studies were performed on highly resolved PSII preparations at pH 7.5 {Kim et al. (1998) Biochim. Biophys. Acta 1364, 337-360; publisher's correction, Biochim. Biophys. Acta 1366, 330-354}. Here, we use kinetics to assign vibrational features to tyrosyl radical, D-., in PSII membranes. EPR and fluorescence controls identify a time regime in which D-. decay occurs independently of redox changes involving the PSII quinone accepters. Difference FT-IR spectra, acquired over this time regime, exhibit decreases in the amplitude of a 1477 cm(-1) line; quantitative comparison with EPR transients supports the assignment to D-.. Conditions, requiring the use of phosphate/formate, have been described for observation of a dissimilar FT-TR spectrum, which has been assigned to tyrosyl radical D-.; this spectrum lacks a 1477 cm(-1) line {Hienerwadel et al. (1997) Biochemistry 36, 14712-14723}. Under these conditions, we have observed (1) an acceleration in the rate of D-. decay and a decrease in D-. yield attributable to the presence of formate, (2) a proportional decrease in the amplitude of FT-IR spectra acquired over the time regime in which D-. decays, (3) frequency shifts in the D-. - D FT-IR spectrum, (4) large-scale structural changes, as assessed by the amide I line shape, and (5) contributions to the FT-LR spectrum from the phosphate/formate buffer in the absence of PSII, We conclude that changes in the FT-IR spectrum, observed in the presence of phosphate/formate, are caused by alterations in the environment of D-. and by direct phosphate/formate contributions to the spectrum. [References: 49]
机译：光系统II（PSII）包含具有氧化还原活性的酪氨酸D。差示傅立叶变换红外光谱可用于获取有关该物质的结构信息，该物质为光氧化形式的中性自由基D-。以前，我们已经使用同位素标记，定点诱变和动力学将1477 cm（-1）处的振动线分配给D-。这些研究是在pH值为7.5的高度分离的PSII制剂上进行的{Kim等。 （1998）Biochim。生物物理学。 Acta 1364，337-360;出版商的更正，Biochim。生物物理学。 Act 1366，330-354}。在这里，我们使用动力学将振动特征分配给PSII膜中的酪氨酰自由基D-。 EPR和荧光控制可识别D-的时间范围。衰变独立于涉及PSII醌受体的氧化还原变化而发生。在此时间范围内获得的差分FT-IR光谱显示出1477 cm（-1）线的振幅减小;与EPR瞬态的定量比较支持将D-分配给D-。已经描述了需要使用磷酸盐/甲酸酯的条件，用于观察不同的FT-TR光谱，该光谱已分配给酪氨酰基D-。该光谱缺少1477 cm（-1）的谱线{Hienerwadel等。 （1997）Biochemistry 36，14712-14723}。在这些条件下，我们已经观察到（1）D-速率的加速。衰减并降低D-。 （2）在D-的时间范围内获得的FT-IR光谱的振幅成比例地降低。衰减，（3）D-中的频移。 -D FT-IR光谱，（4）通过酰胺I线形评估的大规模结构变化，以及（5）在不存在PSII的情况下，磷酸盐/甲酸酯缓冲液对FT-LR光谱的贡献，我们得出结论在磷酸盐/甲酸酯存在下观察到的FT-IR光谱变化是由D-环境的变化引起的。以及磷酸盐/甲酸酯对光谱的直接贡献。 [参考：49]

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