Lipids affect the charge stabilization in wild-type and mutant reaction centers of Rhodobacter sphaeroides R-26

The effect of lipids on stabilization of electrons on the secondary quinone was studied in reaction centers (RC) of herbicide-sensitive and -resistant (L229Ile --> Met) Rhodobacter sphaeroides R-26. The lipid concentration an d the lipid/protein ratio of the intracytoplasmic membranes (ICM) were larg er in the mutant RCs than in the wild-type. The free energy changes of Q(A) (-)Q(B) --> Q(A)Q(B)(-) electron transfer were Delta G(0) = -57 meV, -69 me V, -85 meV for the wild-type and Delta G(0) = 0 meV, -15 meV, -46 meV for t he mutant at pH = 8.0, in detergent, liposome and ICM, respectively. The di fferences in the stabilization energies of both strains decreased from the detergent via proteoliposome to chromatophore. We conclude that the energet ics of the interquinone electron transfer depends on the environment of the reaction center. The steric and/or electrostatic interactions of the envir onment and QB pocket can modulate the energetics of the charge stabilizatio n over large distances. The interaction may have crucial importance on coup ling the electron transport in the photosynthetic membrane to the anabolic/ catabolic processes taking place in the cells.