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首页> 外文期刊>Biochemistry >Identification of a Novel Protonation Pattern for Carboxylic Acids upon Q_B Photoreduction in Rhodobacter sphaeroides Reaction Center Mutants at Asp-L213 and Glu-L212 Sites
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Identification of a Novel Protonation Pattern for Carboxylic Acids upon Q_B Photoreduction in Rhodobacter sphaeroides Reaction Center Mutants at Asp-L213 and Glu-L212 Sites

机译：在球形红球菌反应中心突变体的Asp-L213和Glu-L212位点Q_B光还原后，一种新型的羧酸质子化模式的鉴定

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摘要

In the reaction center from the photosynthetic purple bacterium Rhodobacter sphaeroides,light energy is rapidly converted to chemical energy through coupled electron-proton transfer to a buried quinone molecule QB.Involved in the proton uptake steps are carboxylic acids,which have characteristic infrared vibrations that are observable using light-induced Fourier transform infrared (FTIR) difference spectroscopy.Upon formation,Q_B~- induces protonation of Glu-L212,located within 5 A of QB,resulting in a IR signal at 1728 cm~(-1).However,no other IR signal is observed within the classic absorption range of protonated carboxylic acids (1770-1700 cm~(-1))- In particular,no signal for Asp-L213 is found despite its juxtaposition to QB and importance for proton uptake on the second electron-transfer step.In an attempt to uncover the reason behind this lack of signal,the microscopic electrostatic environment in the vicinity of QB was modified by interchanging Asp and Glu at the L213 and L212 positions.The Q_B~-/Q_B FTIR spectrum of the Asp-L212/Glu-L213 swap mutant in the 1770-1700 cm~(-1) range shows several distinct new signals,which are sensitive to ~1H/~2H isotopic exchange,indicating that the reduction of QB results in the change of the protonation state of several carboxylic acids.The new bands at 1752 and 1747 cm~(-1) were assigned to an increase of protonation in response to QB reduction of Glu-L213 and Asp-L212,respectively,based on the effect of replacing them with their amine analogues.Since other carboxylic acid signals were observed,it is concluded that the swap mutations at L212 and L213 affect a cluster of carboxylic acids larger than the L212/L213 acid pair.Implications for the native reaction center are discussed.
机译：在光合作用紫色细菌球形红细菌的反应中心，光能通过耦合的电子-质子转移到掩埋的醌分子QB迅速转化为化学能。参与质子吸收步骤的是羧酸，羧酸具有特有的红外振动使用光诱导傅立叶变换红外（FTIR）差光谱法可以观察到.Q_B〜-形成后，会诱导Qlu 5 A内Glu-L212的质子化，从而在1728 cm〜（-1）处产生IR信号。在经典的质子化羧酸吸收范围（1770-1700 cm〜（-1））内未观察到其他IR信号-特别是，尽管Asp-L213与QB并置且对于质子吸收质子交换酶很重要，但未发现Asp-L213的信号。为了揭示这种信号不足的原因，试图通过交换L213和L212 p处的Asp和Glu来改变QB附近的微观静电环境。在1770-1700 cm〜（-1）范围内的Asp-L212 / Glu-L213交换突变体的Q_B〜-/ Q_B FTIR谱显示了几个不同的新信号，这些信号对〜1H /〜2H同位素交换敏感，表明QB的还原导致几种羧酸的质子化状态的变化。响应于GB-L213和QB的QB还原，在1752和1747 cm〜（-1）处的新谱带被赋予质子化的增加。 Asp-L212分别基于其胺类似物替代的效果。由于观察到其他羧酸信号，因此得出结论，L212和L213的交换突变会影响比L212 / L213酸大的羧酸簇讨论了本机反应中心的含义。

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