Effects of Oxygen, Heavy Water, and Glycerol on Electron Transfer in the Acceptor Part of Rhodobacter sphaeroides Reaction Centers

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P. P. Knox^1*, M. S. Baptista², A. F. Uchoa², and N. I. Zakharova¹

¹Biology Faculty, Lomonosov Moscow State University, 119992 Moscow, Russia; fax: (7-095) 939-1115; E-mail: knox@biophys.msu.ru

²Departamento de Bioquimica, Instituto de Quimica, Universidade de Sao Paulo, 748, 05508-900 Sao Paulo, SP, Brazil; fax: 55-11-38155579; E-mail: baptista@iq.usp.br

^* To whom correspondence should be addressed.

Received September 3, 2004; Revision received October 6, 2004

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The kinetics of electron transfer between primary and secondary quinone acceptors of the photosynthetic reaction center (RC) of the purple bacterium Rhodobacter sphaeroides wild type was studied at the wavelengths 400 and 450 nm. It was shown that removing of molecular oxygen from RC preparations slowed down the fast phase of the process from 4-4.5 µsec to tens of microseconds. Similar effects were observed after the incubation of RC in heavy water for 72 h or glycerol addition (90% v/v) to RC preparations. The observed effects are interpreted in terms of the influence of these agents on the hydrogen bond system of the RC. The state of this system can determine the formation of different RC conformations that are characterized by different rates of electron transfer between quinone acceptors.

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KEY WORDS: purple bacteria, photosynthetic reaction center, quinone acceptors, electron transport, oxygen, heavy water, glycerol

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