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: email@example.com
* To whom correspondence should be addressed.
Received May 24, 2007; Revision received June 13, 2007
Cooperative interaction of the high-potential hemes (Ch) 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 Ch 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 Ch caused a three- to four-fold acceleration of the electron transfer from the cytochrome subunit to RC.
KEY WORDS: purple bacteria, reaction center, cytochromes, electron transport, mathematical model, Ectothiorhodospira shaposhnikovii