Interaction of Viologen Dyes With Chromatophores and Reaction‐center Preparations From Rhodospirillum Rubrum

Abstract—Various low‐potential viologen dyes enhance light‐induced absorption changes in the near‐infrared region (ΔA870) in chromatophore preparations from Rhodospirillum rubrum in the presence of dichlorophenol indophenol and a high concentration of ascorbate (DCPIP + asc). An increase in ΔA870 was also observed in large reaction‐center preparations from R. rubrum with viologens in the presence of ascorbate. Our results indicate that E'0, of the primary electron acceptor X may be as low as ‐0.37 V, as suggested recently by P. A. Loach (1973, personal communication).