CHARACTERIZATION OF TRIPLET-STATES IN ISOLATED PHOTOSYSTEM-II REACTION CENTERS - OXYGEN QUENCHING AS A MECHANISM FOR PHOTODAMAGE
CHARACTERIZATION OF TRIPLET-STATES IN ISOLATED PHOTOSYSTEM-II REACTION CENTERS - OXYGEN QUENCHING AS A MECHANISM FOR PHOTODAMAGE
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DOI：
10.1016/0005-2728(90)90148-w
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发表时间：
1990-06-01
期刊：
影响因子：
--
通讯作者：
PORTER, G
中科院分区：
文献类型：
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作者：
DURRANT, JR;GIORGI, LB;PORTER, G
瞬时吸收光谱学已被用于研究分离的D1/D2/细胞色素B-559反应中心复合物在4 ℃下的吸收。C. D1/D2反应中心被观察到在有氧条件下对光损伤的敏感性增加。这归因于P680三重态的氧猝灭，这导致形成高氧化性的单氧。观察到该P680三重态的寿命为（1.0 ±-. 0.1)在厌氧条件下缩短至（33. ±. 3)μ s。这种状态，其量子产率约为。30%，通过其最红吸收带的瞬时漂白，其峰值在（680.5 ±）处，被鉴定为驻留在初级电子供体P680上。0.5)nm. P680三重态减单重态吸收差谱的形状，特别是（12. ±. 1)nm带宽的红色吸收带漂白，表明P680可能是一对激子耦合叶绿素分子，与P680三重态被定位在这些叶绿素分子之一。通过P680三重态形成漂白的红色吸收带具有133 000 M-1·cm-1的峰值消光系数和比叶绿素a单体在乙醚中的Qy带的振子强度大1.1倍的振子强度。这表明，该P680三重态主要是通过从4 °的初级自由基对态的电荷复合形成的。C.还观察到3%的量子产率的类胡萝卜素三重态，其特征在于在526 nm处的吸收峰。观察到的P680三联体似乎没有被这种类胡萝卜素淬灭。
Transient absorption spectroscopy has been used to study the isolated D1/D2/cytochrome b-559 reaction centre complex at 4.degree. C. The D1/D2 reaction centre is observed to have an increased susceptibility to photodamage under aerobic conditions. This is attributed to oxygen quenching of a P680 triplet state, which results in the formation of highly oxidising single oxygen. This P680 triplet state is observed to have a lifetime of (1.0 .+-. 0.1) ms under anaerobic conditions, shortening to (33 .+-. 3) .mu.s in the presence of oxygen. This state, which has a quantum yield of approx. 30%, is identified as residing upon the primary electron donor P680 by the transient bleaching of its reddest absorption band, which peaks at (680.5 .+-. 0.5) nm. The shape of the P680 triplet-minus-single absorption difference spectrum, and particualrly the (12 .+-. 1) nm bandwidth of the red absorption band bleach, indicate that P680 is probably a pair of excitonically coupled chlorophyll molecules, with the P680 triplet state being localised upon one of these chlorophyll molecules. The red absorption band bleached by P680 triplet formation has a peak extinction coefficient of 133 000 M-1.cntdot.cm-1 and an oscillator strength 1.1-times larger than that of the Qy-band of a chlorophyll a monomer in ether. It is shown that this P680 triplet state is formed primarily by charge recombination from the primary radical pair state at 4.degree. C. A 3% quantum yield of a carotenoid triple state characterised by an absorption peak at 526 nm is also observed. The observed P680 triplet does not appear to be quenched by this carotenoid.