American Chemical Society
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Internal Electrostatic Control of the Primary Charge Separation and Recombination in Reaction Centers from Rhodobacter sphaeroides Revealed by Femtosecond Transient Absorption

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journal contribution
posted on 2009-08-06, 00:00 authored by K. Gibasiewicz, M. Pajzderska, M. Ziółek, J. Karolczak, A. Dobek
We report the observation of two conformational states of closed RCs from Rhodobacter sphaeroides characterized by different P+HA → PHA charge recombination lifetimes, one of which is of subnanosecond value (700 ± 200 ps). These states are also characterized by different primary charge separation lifetimes. It is proposed that the distinct conformations are related to two protonation states either of reduced secondary electron acceptor, QA, or of a titratable amino acid residue localized near QA. The reaction centers in the protonated state are characterized by faster charge separation and slower charge recombination when compared to those in the unprotonated state. Both effects are explained in terms of the model assuming modulation of the free energy level of the state P+HA by the charges on or near QA and decay of the P+HA state via the thermally activated P+BA state.