Role of PufX in Photochemical Charge Separation in the RC-LH1 Complex from Rhodobacter sphaeroides: An Ultrafast Mid-IR Pump鈥揚robe Investigation

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• 作者：Andreas D. Stahl ; Lucy I. Crouch ; Michael R. Jones ; Ivo van Stokkum ; Rienk van Grondelle ; Marie Louise Groot
• 刊名：The Journal of Physical Chemistry B
• 出版年：2012
• 出版时间：January 12, 2012
• 年：2012
• 卷：116
• 期：1
• 页码：434-444
• 全文大小：625K
• 年卷期：v.116,no.1(January 12, 2012)
• ISSN：1520-5207

文摘

Photochemical charge separation in isolated reaction center-light harvesting 1 (RC-LH1) complexes from Rhodobacter sphaeroides was examined using time-resolved mid-infrared pump鈥損robe spectroscopy. Absorption difference spectra were recorded between 1760 and 1610 cm^鈥? with subpicosecond time resolution to characterize excited-state and radical pair dynamics in these complexes, via the induced absorption changes in the keto carbonyl modes of the bacteriochlorophylls and bacteriopheophytins. Experiments on RC-LH1 complexes with and without the polypeptide PufX show that its presence is required to achieve generation of the radical pair P⁺Q_A^{鈥?/sup> under mildly reducing conditions. In the presence of PufX, the final radical pair formed over a 3 ns period was P+Q_A鈥?/sup>, but in its absence the corresponding radical pair was P+H_A鈥?/sup>, implying that Q_A was either absent in these PufX-deficient complexes or was prereduced. However, P+Q_A鈥?/sup> could be generated in PufX-deficient complexes following addition of the oxidant DMSO, showing that Q_A was present in these complexes and allowing the conclusion that under mildly reducing conditions charge separation was blocked after P+H_A鈥?/sup> due to the presence of an electron on Q_A. The data provide strong support for the hypothesis that one of the functions of PufX is to regulate the stability of Q_B鈥?/sup>, ensuring the oxidation of Q_A鈥?/sup> in the presence of a reduced quinone pool and so preserving efficient photochemical charge separation under anaerobic conditions.}