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On the Involvement of the Water-Polaron Mechanism in Energy Trapping by Reaction Centers of Purple Bacteria

A. Yu. Borisov1* and S. A. Kuznetsova2

1Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 189992 Russia

2Department of Biophysics, School of Physics, Lomonosov Moscow State University, Moscow, 189992 Russia; fax: (095) 939-3181; E-mail: borissov@genebee.msu.su

* To whom correspondence should be addressed.

Received October 15, 2001; Revision received June 26, 2002
A locus for binding a mobile water molecule was searched for in the immediate vicinity of the special pair in the reaction center. Using the PROTEUS PC-program (a part of the GRASP package) atomic structures of the reaction centers were analyzed in purple bacteria Rhodopseudomonas viridis and Rhodobacter sphaeroides. In both structures the loci for binding mobile water molecules were found at the distance of about 4.5 Å from the middle of the special pair in the reaction center. The reorientation of a hydrogen atom of this water molecule in the electric field of the excited special pair required energy of no less than 40 MeV that corresponded to predictions of the water-polarization model of trapping of electron excitation which was developed by M. V. Fok and one of the authors of this article.
KEY WORDS: purple bacteria, reaction centers, electron excitation trapping, water-polarization and exciton mechanisms