Electron transfer in pheophytin a‐modified reaction centers from Rhodobacter sphaeroides (R‐26)

[摘要]

The major part (> 90%) of bacteriopheophytin a in reaction centers (RCs) of Rhodobacter sphaeroides was substituted by plant pheophytin a. In modified RCs the photochemical formation of P⁺Q_a ⁻ occurs with with a quantum efficiency of 79%. The intermediary state P⁺I⁻ displayed a recombination time constant of 1.5 ns, and the electron transfer from I⁻ to Q_a was characterized by a time constant of 540 ps. On the basis of spectral properties of P⁺I⁻ for native and modified RCs, it was suggested that bacteriopheophytin, as well as bacteriochlorophyll monomers located in L protein branch, have a transition at 545 nm with approx. equal extinction coefficients. Accordingly, the state P⁺I⁻ in modified RCs is proposed to consist of a thermodynamic mixture of P⁺BL⁻ (∼ 80%) and P⁺Phe⁻ (∼ 20%).

[学科分类] 生物化学/生物物理

[关键词] Reaction center;Primary electron donor and acceptor;Electron transfer;Bacteriopheophytin;Pheophytin;Rhodobacter sphaeroides;BChl;BPhe;Chl and Phe;bacteriochlorophyll a;bacteriopheophytin a;chlorophyll a and pheophytin a;respectively;BL and BM;bacteriochlorophyll monomers located in L and M protein subunits;respectively;HL and HM;bacteriopheophytins in L and M subunits;respectively;P;primary electron donor;bacteriochlorophyll dimer;Qa and Qb;primary and secondary quinons;respectively;Qy and Qx;first and second electronic transitions in Chl-like molecules;respectively;RCs;reaction centers