Limantara L, Fujii R, Zhang J P, Kakuno T, Hara H, Kawamori A, Yagura T, Cogdell R J, Koyama Y
Faculty of Science, Kwansei Gakuin University, Nishinomiya, Japan.
Biochemistry. 1998 Dec 15;37(50):17469-86. doi: 10.1021/bi981803q.
The LH1 antenna complex and a native form of the LH2 complex were isolated from the carotenoidless R26 and R26.1 mutants of Rhodobacter sphaeroides by the use of a new detergent, sucrose monocholate. One-color, pump-and-probe transient Raman spectroscopy of these complexes using 351 nm, approximately 50 ps pulses showed the generation of the triplet state of bacteriochlorophyll a (BChl a), whereas measurements using 355 nm, approximately 12 ns pulses showed the generation of BChl a cation radical. Subpicosecond to nanosecond time-resolved absorption spectroscopy using 388 nm, 200 fs pulses for excitation showed rapid (<1 ps) generation of the triplet state and fast decay (<10 ps) of the singlet state of BChl a. Microsecond absorption spectroscopy confirmed the generation of BChl a cation radical. EPR spectroscopy using 532 nm, approximately 5 ns pulses for excitation established the generation of BChl a cation radical. The EPR line width suggested that the unpaired electron is shared by two BChl a molecules. In LH1, the yield of BChl a cation radical per complex was estimated to be about 80% of that in the reaction center, and in LH2 about 50%. Thus, rapid generation of the triplet state, and its subsequent transformation into the cation-radical state of BChl a have been shown to be intrinsic properties of B870 and B850 BChl a assembly in the carotenoidless LH1 and LH2 antenna complexes. In the case of the carotenoid-containing LH2 complex, the triplet states of BChl a and carotenoid (spheroidene) were generated immediately after excitation, but the triplet-state BChl a was quenched efficiently by the carotenoid so that no BChl a cation radical was generated. Thus, the photoprotective function of the carotenoid in this antenna complex is shown.
使用新型去污剂单胆酸蔗糖，从球形红细菌无类胡萝卜素的R26和R26.1突变体中分离出LH1天线复合物和天然形式的LH2复合物。使用351 nm、约50 ps脉冲对这些复合物进行单色泵浦-探测瞬态拉曼光谱，结果显示生成了细菌叶绿素a（BChl a）的三重态，而使用355 nm、约12 ns脉冲进行测量则显示生成了BChl a阳离子自由基。使用388 nm、200 fs脉冲进行激发的亚皮秒至纳秒时间分辨吸收光谱显示，BChl a的三重态快速生成（<1 ps），单重态快速衰减（<10 ps）。微秒吸收光谱证实了BChl a阳离子自由基的生成。使用532 nm、约5 ns脉冲进行激发的电子顺磁共振光谱确定了BChl a阳离子自由基的生成。电子顺磁共振线宽表明未成对电子由两个BChl a分子共享。在LH1中，每个复合物中BChl a阳离子自由基的产率估计约为反应中心的80%，在LH2中约为50%。因此，三重态的快速生成及其随后向BChl a阳离子自由基态的转变已被证明是无类胡萝卜素LH1和LH2天线复合物中B870和B850 BChl a聚集体的固有特性。在含类胡萝卜素的LH2复合物中，激发后立即生成了BChl a和类胡萝卜素（球形烯）的三重态，但类胡萝卜素有效地淬灭了三重态BChl a，因此未生成BChl a阳离子自由基。因此，展示了该天线复合物中类胡萝卜素的光保护功能。
