Cooperative Interaction of High-Potential Hemes in the Cytochrome Subunit of the Photosynthetic Reaction Center of Bacterium Ectothiorhodospira shaposhnikovii

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I. I. Pottosin¹, C. S. Chamorovsky², and S. K. Chamorovsky^3*

¹Centro Universitario de Investigaciones Biomedicas, Universidad de Colima, Colima, Mexico

²Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia

³Department of Biophysics, Biology Faculty, Lomonosov Moscow State University, 119992 Moscow, Russia; fax: (495) 939-1115; E-mail: chamorovsky@biophys.msu.ru

^* To whom correspondence should be addressed.

Received May 24, 2007; Revision received June 13, 2007

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Cooperative interaction of the high-potential hemes (C_h) in the cytochrome subunit of the photosynthesizing bacterium Ectothiorhodospira shaposhnikovii was studied by comparing redox titration curves of the hemes under the conditions of pulse photoactivation inducing single turnover of electron-transport chain and steady-state photoactivation, as well as by analysis of the kinetics of laser-induced oxidation of cytochromes by reaction center (RC). A mathematical model of the processes of electron transfer in cytochrome-containing RC was considered. Theoretical analysis revealed that the reduction of one heme C_h facilitated the reduction of the other heme, which was equivalent to a 60 mV positive shift of the midpoint potential. In addition, reduction of the second heme C_h caused a three- to four-fold acceleration of the electron transfer from the cytochrome subunit to RC.

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KEY WORDS: purple bacteria, reaction center, cytochromes, electron transport, mathematical model, Ectothiorhodospira shaposhnikovii

DOI: 10.1134/S0006297907110120

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