Comparison of M-Side Electron Transfer in Rb. sphaeroides and Rb. capsulatus Reaction Centers

• DOI: 10.1021/jp013264w
• Publication Date: 2002-07-26T04:48:01Z
• Authors: Christine Kirmaier; Philip D. Laible; Kazimierz Czarnecki; Aaron N. Hata; Deborah K. Hanson; David F. Bocian; Dewey Holten
• Keywords: Rhodobacter sphaeroides; Rhodobacter; Side chain

Subpicosecond time-resolved absorption and steady-state resonance Raman studies are reported for Rhodobacter sphaeroides reaction centers (RCs) that incorporate the G(M203)D/L(M214)H double mutation (denoted DH). Upon excitation, P* decays with a time constant of 15 ps via combination electron transfer to L side (83%), decay ground state (10%), M form P+BPhM- (7%). On L-side, branching between charge recombination versus separation at transient intermediate reduces subsequent P+QA- yield 68%. These results differ in detail from those found previously Rb. capsulatus G(M201)D/L(M212)H analogue (also denoted DH), most notably 2-fold lower M-side sphaeroides. Studies on DH mutant carotenoidless strain give same spectral signatures carotenoid-containing mutant. This finding eliminates any possibility QX bleaching assigned reduction BPhM is compromised by carotenoid bandshifts resulting simply L-side separation. The collective reveal significant differences rates (as well as side) sphaeroides, which must arise some or large measure small (perhaps tens meV) free energies states two species. relative turn derive cofactor-protein interactions (in both wild type mutants), indicated data. species have insignificant (though observable) effects primary events wild-type RCs, but greater consequences when modest energy gaps further reduced mutants. RCs may general propensity normally inactive branch, compared capsulatus.