Cogdell R J, Monger T G, Parson W W
Biochim Biophys Acta. 1975 Dec 11;408(3):189-99. doi: 10.1016/0005-2728(75)90122-x.
Purified photochemical reaction centers from three strains of Rhodopseudomonas sphaeroides and two of Rhodospirillium rubrum were reduced with Na2S2O4 so as to block their photochemical electron transfer reactions. They then were excited with flashes lasting 5-30 ns. In all cases, absorbance measurements showed that the flash caused the immediate formation of a transient state (PF) which had been detected previously in reaction centers from Rps. sphaeroides strain R26. Previous work has shown that state PF is an intermediate in the photochemical electron transfer reaction in the reaction centers of that particular strain, and the present work generalizes that conclusion. In the reaction centers from two strains that lack carotenoids (Rps. sphaeroides R26 and R. rubrum G9), the decay of PF yields a longer-lived state (PR) which is probably a triplet state of the bacteriochlorophyll of the reaction center. In the R26 preparation, the decay of PF was found to have a half-time of 10 +/- 2 ns. The decay kinetics rule out the identification of PF as the fluorescent excited singlet state of the reaction center. In the reaction centers from three strains that contain carotenoids (Rps sphaeroides 2.4.1 and Ga, and R. rubrum S1), state PR was not detected, and the decay of PF generated triplet states of carotenoids. The efficiency of the coupling between the decay of PF and the formation of the carotenoid triplet appeared to be close to 100% at room temperature, but somewhat lower at 77 degrees K. Taken with previous results, this suggests that the coupling is direct and does not require the intermediate formation of state PR. This conclusion would be consistent with the view that PF is a biradical which can be triplet in character.
来自三株球形红假单胞菌和两株深红红螺菌的纯化光化学反应中心用连二亚硫酸钠还原，以阻断其光化学电子转移反应。然后用持续5 - 30纳秒的闪光激发它们。在所有情况下，吸光度测量表明，闪光导致了一种瞬态（PF）的立即形成，这种瞬态先前已在球形红假单胞菌R26菌株的反应中心中检测到。先前的工作表明，状态PF是该特定菌株反应中心光化学电子转移反应中的一个中间体，而本研究将该结论推广到了其他菌株。在两株缺乏类胡萝卜素的菌株（球形红假单胞菌R26和深红红螺菌G9）的反应中心中，PF的衰减产生了一个寿命更长的状态（PR），它可能是反应中心细菌叶绿素的三重态。在R26制剂中，发现PF的衰减半衰期为10±2纳秒。衰减动力学排除了将PF鉴定为反应中心荧光激发单重态的可能性。在三株含有类胡萝卜素的菌株（球形红假单胞菌2.4.1和Ga，以及深红红螺菌S1）的反应中心中，未检测到状态PR，PF的衰减产生了类胡萝卜素的三重态。在室温下，PF的衰减与类胡萝卜素三重态的形成之间的耦合效率似乎接近100%，但在77K时略低。结合先前的结果，这表明这种耦合是直接的，不需要中间形成状态PR。这一结论与PF是一种具有三重态特征的双自由基的观点一致。
