Conjugation-length dependence of the T1 lifetimes of carotenoids free in solution and incorporated into the LH2, LH1, RC, and RC-LH1 complexes: possible mechanisms of triplet-energy dissipation.
Conjugation-length dependence of the T1 lifetimes of carotenoids free in solution and incorporated into the LH2, LH1, RC, and RC-LH1 complexes: possible mechanisms of triplet-energy dissipation.
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DOI：
10.1021/bi062237z
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发表时间：
2007-01
期刊：
影响因子：
2.9
通讯作者：
Yoshinori Kakitani;Junji Akahane;H. Ishii;H. Sogabe;H. Nagae;Y. Koyama
中科院分区：
文献类型：
--
作者：
Yoshinori Kakitani;Junji Akahane;H. Ishii;H. Sogabe;H. Nagae;Y. Koyama
除了抗氧化剂和间隔物的作用外，紫色光合细菌中的类胡萝卜素（Cars）还追求两种生理功能，即光捕获和光保护。为了揭示光保护功能的机制，即猝灭三重态细菌叶绿素以防止单线态氧的敏化产生，记录了Cars的三重态吸收光谱，其中共轭双键（n）的数量（n）在9-13范围内，以确定三重态寿命对n的依赖性。所检查的汽车包括 (a) 解决方案中的汽车； (b) 重建的 LH1 复合物； (c) 来自 Rba 的天然 LH2 复合物。球状体G1C、Rba。球状体2.4.1，Rsp。 molischianum 和 Rps。嗜酸菌 10050; (d) Rba 的 RC。球状体G1C、Rba。球状体2.4.1和Rsp。红色 S1; (e) 来自 Rba 的 RC-LH1 复合物。球状体G1C、Rba。球状体2.4.1，Rsp。莫利斯奇安姆，Rps。嗜酸菌 10050 和 Rsp。红色 S1。结果使我们提出以下机制：（i）从溶液到 LH2 复合物的线性依赖性对较短寿命的实质性转变归因于 Car 共轭链的扭曲。 (ii)从重构的LH1到RC-LH1复合物的LH1组分的线性依赖性斜率的显着降低归因于次要组分Car形成三重态能量的泄漏通道。 (iii)从分离的RC到RC-LH1复合物的RC组分的共轭长度依赖性的丧失归因于RC组分中由细菌叶绿素组成的三重态能量库的存在。
In addition to the roles of antioxidant and spacer, carotenoids (Cars) in purple photosynthetic bacteria pursue two physiological functions, i.e., light harvesting and photoprotection. To reveal the mechanisms of the photoprotective function, i.e., quenching triplet bacteriochlorophyll to prevent the sensitized generation of singlet oxygen, the triplet absorption spectra were recorded for Cars, where the number of conjugated double bonds (n) is in the region of 9-13, to determine the dependence on n of the triplet lifetime. The Cars examined include those in (a) solution; (b) the reconstituted LH1 complexes; (c) the native LH2 complexes from Rba. sphaeroides G1C, Rba. sphaeroides 2.4.1, Rsp. molischianum, and Rps. acidophila 10050; (d) the RCs from Rba. sphaeroides G1C, Rba. sphaeroides 2.4.1, and Rsp. rubrum S1; and (e) the RC-LH1 complexes from Rba. sphaeroides G1C, Rba. sphaeroides 2.4.1, Rsp. molischianum, Rps. acidophila 10050, and Rsp. rubrum S1. The results lead us to propose the following mechanisms: (i) A substantial shift of the linear dependence to shorter lifetimes on going from solution to the LH2 complex was ascribed to the twisting of the Car conjugated chain. (ii) A substantial decrease in the slope of the linear dependence on going from the reconstituted LH1 to the LH1 component of the RC-LH1 complex was ascribed to the minor-component Car forming a leak channel of triplet energy. (iii) The loss of conjugation-length dependence on going from the isolated RC to the RC component of the RC-LH1 complex was ascribed to the presence of a triplet-energy reservoir consisting of bacteriochlorophylls in the RC component.