Farhoosh R, Chynwat V, Gebhard R, Lugtenburg J, Frank H A
Department of Chemistry, Saint Joseph College, West Hartford, CT, USA.
Photochem Photobiol. 1997 Jul;66(1):97-104. doi: 10.1111/j.1751-1097.1997.tb03144.x.
Three carotenoids, spheroidene, 3,4-dihydrospheroidene and 3,4,5,6-tetrahydrospheroidene, having 8, 9 and 10 conjugated carbon-carbon double bonds, respectively, were incorporated into Rhodobacter (Rb.) sphaeroides R-26.1 reaction centers. The extents of binding were found to be 95 +/- 5% for spheroidene, 65 +/- 5% for 3,4-dihydrospheroidene and 60 +/- 10% for 3,4,5,6-tetrahydrospheroidene. The dynamics of the triplet states of the primary donor and carotenoid were measured at room temperature by flash absorption spectroscopy. The carotenoid, spheroidene, was observed to quench the primary donor triplet state. The triplet state of spheroidene that was formed subsequently decayed to the ground state with a lifetime of 7.0 +/- 0.5 microseconds. The primary donor triplet lifetime in the Rb. sphaeroides R-26.1 reaction centers lacking carotenoids was 60 +/- 5 microseconds. Quenching of the primary donor triplet state by the carotenoid was not observed in the Rb. sphaeroides R-26.1 reaction centers containing 3,4-dihydrospheroidene nor in the R-26.1 reaction centers containing 3,4,5,6-tetrahydrospheroidene. Triplet-state electron paramagnetic resonance was also carried out on the samples. The experiments revealed carotenoid triple-state signals in the Rb. sphaeroides R-26.1 reaction centers incorporated with spheroidene, indicating that the primary donor triplet is quenched by the carotenoid. No carotenoid signals were observed from Rb. sphaeroides R-26.1 reaction centers incorporating 3,4-dihydrospheroidene nor in reaction centers incorporating 3,4,5,6-tetrahydrospheroidene. Circular dichroism, steady-state absorbance band shifts accompanying the primary photochemistry in the reaction center and singlet energy transfer from the carotenoid to the primary donor confirm that the carotenoids are bound in the reaction centers and interacting with the primary donor. These studies provide a systematic approach to exploring the effects of carotenoid structure and excited-state energy on triplet transfer between the primary donor and carotenoids in reaction centers from photosynthetic bacteria.
三种分别具有8个、9个和10个共轭碳 - 碳双键的类胡萝卜素，即球形烯、3,4 - 二氢球形烯和3,4,5,6 - 四氢球形烯，被掺入到球形红细菌（Rb.）球形红细菌R - 26.1的反应中心。发现球形烯的结合程度为95±5%，3,4 - 二氢球形烯为65±5%，3,4,5,6 - 四氢球形烯为60±10%。通过闪光吸收光谱在室温下测量了初级供体和类胡萝卜素三重态的动力学。观察到类胡萝卜素球形烯淬灭了初级供体三重态。随后形成的球形烯三重态以7.0±0.5微秒的寿命衰减到基态。在不含类胡萝卜素的球形红细菌R - 26.1反应中心中，初级供体三重态寿命为60±5微秒。在含有3,4 - 二氢球形烯的球形红细菌R - 26.1反应中心或含有3,4,5,6 - 四氢球形烯的R - 26.1反应中心中，未观察到类胡萝卜素对初级供体三重态的淬灭。还对样品进行了三重态电子顺磁共振实验。实验揭示了在掺入球形烯的球形红细菌R - 26.1反应中心中存在类胡萝卜素三重态信号，表明初级供体三重态被类胡萝卜素淬灭。在掺入3,4 - 二氢球形烯的球形红细菌R - 26.1反应中心或掺入3,4,5,6 - 四氢球形烯的反应中心中未观察到类胡萝卜素信号。圆二色性、伴随反应中心初级光化学的稳态吸收带位移以及从类胡萝卜素到初级供体的单线态能量转移证实了类胡萝卜素结合在反应中心并与初级供体相互作用。这些研究提供了一种系统的方法来探索类胡萝卜素结构和激发态能量对光合细菌反应中心中初级供体和类胡萝卜素之间三重态转移的影响。
