Kinetics of electron transfer between the primary and the secondary electron acceptor in reaction centers from Rhodopseudomonas sphaeroides

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Photoreduction of the two ubiquinone molecules, UQ 1 and UQ 2, bound to purified reaction center from Rhodopseudomonas sphaeroides induces different absorption band shifts of bacteriochlorophyll and bacteriopheophytin molecules depending on which ubiquinone is photoreduced. This allows us to study electron transfer between UQ 1 and UQ 2 directly by absorption spectrometry. The results support a model in which electrons are transferred one by one from UQ 1 to UQ 2 with a half-time of 200 μs, and two by two from fully reduced UQ 2 to the secondary acceptor pool.