Steady-state FTIR spectra of the photoreduction of QA and QB in Rhodobacter sphaeroides reaction centers provide evidence against the presence of a proposed transient electron acceptor X between the two quinones.
Steady-state FTIR spectra of the photoreduction of QA and QB in Rhodobacter sphaeroides reaction centers provide evidence against the presence of a proposed transient electron acceptor X between the two quinones.
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球形红杆菌反应中心中 QA 和 QB 光还原的稳态 FTIR 光谱提供了证据，证明两个醌之间存在拟议的瞬态电子受体 X。
DOI：
10.1021/bi700297b
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发表时间：
2007
期刊：
影响因子：
2.9
通讯作者：
J. Breton
中科院分区：
文献类型：
--
作者：
J. Breton
在光合细菌球形红杆菌的反应中心 (RC) 中，两个泛醌分子 QA 和 QB 通过耦合电子转移和质子吸收，在光能转化为化学自由能方面发挥着关键作用。在原生 RC 中，电子从 QA 到 QB 的转移发生在 5-200 微秒的时间范围内。基于天然 RC 中时间分辨 FTIR 步进扫描测量，提出了一种新的非传统机制，其中 QB 形成先于 QA 氧化 [Remy, A., and Gerwert, K. (2003) Nat.结构。生物。 10, 637-644]。最近通过快速扫描技术在 DN(L210) 突变体 RC 中测量了在 QA 和 QB 之间运行的瞬态中间电子受体（表示为 X）的红外特征，其中 QA 到 QB 的电子转移比天然 RC 减慢了 8 倍。该红外特征已被报道为涉及状态 X+、X、QA 和 QA- 的差异光谱[Hermes, S., et al. (2006) 生物化学 45, 13741-13749]。在这里，我们报告了在亚铁氰化钾存在的情况下在天然和 DN(L210) 突变体 RC 中测量的 QA 或 QB 光还原的稳态 FTIR 差异光谱。在这些光谱中，亚铁氰化物和铁氰化物的 CN 伸缩标记模式可以定量比较氧化还原反应的程度，并用于 QA-/QA 和 QB-/QB 差异光谱的精确归一化。 DN(L210) 突变体 RC 中计算的 QA- QB/QA QB- 双差谱与快速扫描测量中报告的 QA- X+/QA X 谱非常相似。因此，我们得出结论，物种 X+ 和 X 在光谱上分别与 QB 和 QB- 无法区分。进一步比较天然和 DN(L210) RC 中的 QA-QB/QA QB- 双差光谱也可以排除天然 RC 中 QB- 形成先于 QA- 再氧化的可能性。
In the reaction center (RC) of the photosynthetic bacterium Rhodobacter sphaeroides, two ubiquinone molecules, QA and QB, play a pivotal role in the conversion of light energy into chemical free energy by coupling electron transfer to proton uptake. In native RCs, the transfer of an electron from QA to QB takes place in the time range of 5-200 micros. On the basis of time-resolved FTIR step-scan measurements in native RCs, a new and unconventional mechanism has been proposed in which QB- formation precedes QA- oxidation [Remy, A., and Gerwert, K. (2003) Nat. Struct. Biol. 10, 637-644]. The IR signature of the proposed transient intermediary electron acceptor (denoted X) operating between QA and QB has been recently measured by the rapid-scan technique in the DN(L210) mutant RCs, in which the QA to QB electron transfer is slowed 8-fold compared to that in native RCs. This IR signature has been reported as a difference spectrum involving states X+, X, QA, and QA- [Hermes, S., et al. (2006) Biochemistry 45, 13741-13749]. Here, we report the steady-state FTIR difference spectra of the photoreduction of either QA or QB measured in both native and DN(L210) mutant RCs in the presence of potassium ferrocyanide. In these spectra, the CN stretching marker modes of ferrocyanide and ferricyanide allow the extent of the redox reactions to be quantitatively compared and are used for a precise normalization of the QA-/QA and QB-/QB difference spectra. The calculated QA- QB/QA QB- double-difference spectrum in DN(L210) mutant RCs is closely equivalent to the reported QA- X+/QA X spectrum in the rapid-scan measurement. We therefore conclude that species X+ and X are spectrally indistinguishable from QB and QB-, respectively. Further comparison of the QA- QB/QA QB- double-difference spectra in native and DN(L210) RCs also allows the possibility that QB- formation precedes QA- reoxidation to be ruled out for native RCs.