Role of B800 in carotenoid-bacteriochlorophyll energy and electron transfer in LH2 complexes from the purple bacterium Rhodobacter sphaeroides.
Role of B800 in carotenoid-bacteriochlorophyll energy and electron transfer in LH2 complexes from the purple bacterium Rhodobacter sphaeroides.
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B800 在紫色细菌球形红杆菌 LH2 复合物中类胡萝卜素-细菌叶绿素能量和电子转移中的作用。
DOI：
10.1021/jp071395c
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
Frank,HarryA
中科院分区：
文献类型：
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作者：
Polivka,Tomas;Niedzwiedzki,Dariusz;Fuciman,Marcel;Sundstrom,Villy;Frank,HarryA
利用飞秒时间分辨瞬态吸收光谱研究了B800在LH 2络合物中的能量和电子转移作用。利用十二烷基硫酸锂（LDS）对B800位点进行干扰，并通过比较处理和未处理的类胡萝卜素类球红杆菌（Rhodobacter sphaeroides）与类胡萝卜素类神经孢子烯、类球烯和类球蛋白酮的LH 2复合物，探讨B800在类胡萝卜素向细菌叶绿素a（BChla）能量传递和类胡萝卜素自由基形成中的作用. LDS处理的复合物中S1介导的能量转移的效应分别为86%，61%和57%，在LH 2复合物含有neurosporene，spheroidene，spheroidone，分别。类胡萝卜素S1在溶液中的寿命分析，LDS处理，和未处理的LH 2复合物允许确定B800/B850分支比在S1介导的能量转移。结果表明，B800是一个主要的受体，约60%的能量从类胡萝卜素S1状态接受B800。该值几乎与类胡萝卜素的共轭长度无关。除了其在能量传递中的作用，B800 BChlais的唯一的电子受体在类胡萝卜素和BChlain LH 2复合物之间的电荷分离的事件中，这是通过防止类胡萝卜素自由基形成的LDS处理的LH 2复合物证明。在未处理的含有链孢烯和类球烯的复合物中，类胡萝卜素自由基以300−400 fs的时间常数形成。应用不同的激发波长和强度依赖性的类胡萝卜素自由基的形成表明，类胡萝卜素自由基只能形成后，激发的S2状态的类胡萝卜素，虽然S2状态本身不是一个前体的电荷分离状态。相反，无论是热的S1状态或电荷转移状态之间的类胡萝卜素的S2和S1状态被讨论作为潜在的前体的电荷分离状态。
The role of the B800 in energy and electron transfer in LH2 complexes has been studied using femtosecond time-resolved transient absorption spectroscopy. The B800 site was perturbed by application of lithium dodecyl sulfate (LDS), and comparison of treated and untreated LH2 complexes fromRhodobacter sphaeroidesincorporating carotenoids neurosporene, spheroidene, and spheroidenone was used to explore the role of B800 in carotenoid to bacteriochlorophyll-a(BChla) energy transfer and carotenoid radical formation. Efficiencies of the S1-mediated energy transfer in the LDS-treated complexes were 86, 61, and 57% in the LH2 complexes containing neurosporene, spheroidene, and spheroidenone, respectively. Analysis of the carotenoid S1lifetimes in solution, LDS-treated, and untreated LH2 complexes allowed determination of B800/B850 branching ratio in the S1-mediated energy transfer. It is shown that B800 is a major acceptor, as approximately 60% of the energy from the carotenoid S1state is accepted by B800. This value is nearly independent of conjugation length of the carotenoid. In addition to its role in energy transfer, the B800 BChlais the only electron acceptor in the event of charge separation between carotenoid and BChlain LH2 complexes, which is demonstrated by prevention of carotenoid radical formation in the LDS-treated LH2 complexes. In the untreated complexes containing neurosporene and spheroidene, the carotenoid radical is formed with a time constant of 300−400 fs. Application of different excitation wavelengths and intensity dependence of the carotenoid radical formation showed that the carotenoid radical can be formed only after excitation of the S2state of carotenoid, although the S2state itself is not a precursor of the charge-separated state. Instead, either a hot S1state or a charge-transfer state lying between S2and S1states of the carotenoid are discussed as potential precursors of the charge-separated state.