Hystons, new quasi-particles, and electron transfer in bacterial photosynthesis

Abstract

For photosynthetic purple bacteria the collective vibrations of the linked polar fragments and polar elements both in the LH2 antenna complex and reaction center (RC) with their protein environment are described as a motion of hystons, new quasi-particles. Taking into account the fact that hystons modulate the frequency of exciton transitions, the half-width of absorption spectra had been defined as a function of the difference in permanent dipole moment between excited and ground states. Obtained equations for the temperature dependence of full half-width provide an excellent fit to known experimental data for B800 spectra of Rb. sphaeroides and Rps. acidophila as well as for P870 primary electron donor band of Rb. sphaeroides with 63, 52 and 142 cm-1 hyston modes, respectively. The theory has been extended and applied to the calculation of temperature dependence at the rate of electron transfer (ET). After fitting to known data, it has been shown that the 304( ± 10) cm-1 hyston mode, localized mainly on the bacterioheophytin, governs the secondary ET (from the bacterioheophytin to ubiquinone) in the Rps. sphaeroides RC. It is also shown that the primary ET in the RCs of Rps. viridis and Rb. sphaeroides are controlled by special pair pseudo-hyston modes with frequencies 139( ± 11) and 166( ± 28) cm-1, respectively. © 2002 elsevier Science B.V. All rights reserved.