title: Energetics and mechanisms of high efficiency of charge separation and electron transfer processes in Rhodobacter sphaeroides reaction centers.
abstract: Effects of environmental changes due to D(2)O/H(2)O substitution and cryosolvent addition on the energetics of the special pair and the rate constants of forward and back electron transfer reactions in the picosecond-nanosecond time domain have been studied in isolated reaction centers (RC) of the anaxogenic purple bacterium Rhodobacter sphaeroides. The following results were obtained: (i). replacement of H(2)O by D(2)O or addition of either 70% (v/v) glycerol or 35% (v/v) DMSO do not influence the absorption spectra; (ii). in marked contrast to this invariance of absorption, the maxima of fluorescence spectra are red shifted relative to control by 3.5, 6.8 and 14.5 nm for RCs suspended in glycerol, D(2)O or DMSO, respectively; (iii). D(2)O/H(2)O substitution or DMSO addition give rise to an increase of the time constants of charge separation (tau(e)), and Q(A)(-) formation (tau(Q)) by a factors of 2.5-3.1 and 1.7-2.5, respectively; (iv). addition of 70% glycerol is virtually without effect on the values of tau(e) and tau(Q); (v). the midpoint potential E(m) of P/P(+) is shifted by about 30 and 45 mV towards higher values by addition of 70% glycerol and 35% DMSO, respectively, but remains invariant to D(2)O/H(2)O exchange; and (vi). an additional fast component with tau(1)=0.5-0.8 ns in the kinetics of charge recombination P(+)H(A)(-)-->P*(P)H(A) emerges in RC suspensions modified either by D(2)O/H(2)O substitution or by DMSO treatment. The results have been analysed with special emphasis on the role of deformations of hydrogen bonds for the solvation mechanism of nonequilibrium states of cofactors. Reorientation of hydrogen bonds provides the major contribution of the very fast environmental response to excitation of the special pair P. The Gibbs standard free energy gap between 1P* and P(+)B(A)(-) due to solvation is estimated to be approximately 70, 59 and 48 meV for control, D(2)O- and DMSO-treated RC samples, respectively.
authors.affiliation: Department of Biophysics, Biology Faculty, Lomonosov State University, Moscow 119899, Russia. paschenko@biophys.msu.ru
authors.forename: Vladimir Z
authors.initials: VZ
authors.lastname: Paschenko
authors.forename: Vladimir V
authors.initials: VV
authors.lastname: Gorokhov
authors.forename: Peter P
authors.initials: PP
authors.lastname: Knox
authors.forename: Pavel M
authors.initials: PM
authors.lastname: Krasilnikov
authors.forename: Harald
authors.initials: H
authors.lastname: Redlin
authors.forename: Gernot
authors.initials: G
authors.lastname: Renger
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Rubin
mesh_terms: D001429:Bacteriochlorophylls / Q000737:chemistry* / Q000378:metabolism; D017666:Deuterium Oxide / Q000737:chemistry; D004121:Dimethyl Sulfoxide / Q000737:chemistry; D004579:Electron Transport; D005990:Glycerol / Q000737:chemistry; D007700:Kinetics; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism; D012242:Rhodobacter sphaeroides / Q000737:chemistry* / Q000378:metabolism; D012997:Solvents; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics
chemical_list: D001429:Bacteriochlorophylls; D045322:Photosynthetic Reaction Center Complex Proteins; D012997:Solvents; D017666:Deuterium Oxide; D005990:Glycerol; D004121:Dimethyl Sulfoxide