−ΔG and Temperature Dependencies of the Electron Transfer Rates Between P700⁺ and A₁ ⁻ or FeS⁻ in Photosystem I Containing Different Quinones

Abstract

The rate of the electron transfer (ET) between P700+ and A₁ − or P700+ and FeS+ (F_x, F_A and F_B) have been studied in the plant photosystem I reaction center complex that contains different artificial quinones, at 77–277 K by transient absorption spectroscopy and ESR. We reconstituted different artificial quinones after the extraction of the intrinsic A₁ phylloquinone by the ether extraction method. The redox potential of artificial quinones at the A₁−site are between −1 and −0.4 V in contrast to the case of phylloquinone (about −0.8 V). We investigated the rates of charge recombination (CR) from A₁ − or FeS− to P700+ in these RCs, as well as of the ET between A₁ − and FeS.

We obtained the following results: (1) The CR from A₁ − to P700+ showed almost no −ΔG and temperature dependencies with time constants of 150–350 μs. (2) The CR rates from FeS− to P700+ slowed down with decreasing temperature (t₁/_e = 0.03−1 s at 277–77 K).

From these results, we will discuss the ET mechanism between A₁ −, FeS− and P700+.