Figure 1.

(A) Schematic representation of the binding site for PhQ_A (orange), highlighting the main cofactor-protein interactions. Also shown is the iron-sulfur center F_X (S: yellow, Fe: violet). (B and C) Kinetics of PhQ⁻ oxidation monitored at 395 nm in the control strain (B) or PsaA-F689N mutant (C). Solid symbols are the experimental results and the thick solid line is the fit to a sum of exponential functions. Also shown are the contributions of the decay components ascribed primarily to oxidation of ${\text{PhQ}}_{\text{B}}^{-}$ (blue, 24 ns in the WT and 13 ns in the mutant), oxidation of ${\text{PhQ}}_{\text{A}}^{-}$ (red, 256 ns in the WT and 17 μs in the mutant), inter-FeS cluster ET (gold, 184 ns in the mutant), and reduction of ${\text{P}}_{700}^{+}$ (the latter is actually the sum of the ∼6 μs and ∼55 μs components). Note that the ∼180 ns component due to inter-FeS cluster ET is not resolvable in the WT. Data are normalized on same total amplitude and same initial intensity. To see this figure in color, go online.