Study of electrogenic electron transfer steps in chromatophore membrane of Chromatium vinosum by the response of merocyanin dye.

1. Electrogenic steps in photosynthetic cyclic electron transport in chromatophore membrane of Chromatium vinosum were studied by measuring absorption changes of added merocyanin dye and of intrinsic carotenoid. 2. The change in dye absorbance was linear with the membrane potential change induced either by light excitation or by application of diffusion potential by adding valinomycin in the presence of K+ concentration gradient. 3. It was estimated that chromatophore membrane became 40--60 mV and 110--170 mV inside positive upon single and multiple excitations with single-turnover flashes, respectively, from the responses of the dye and the carotenoid. 4. Electron transfers between cytochrome c-555 or c-552 and reaction center bacteriochlorophyll dimer (BChl2) and between BChl2 and the primary electron acceptor were concluded to be electrogenic from the redox titration of the dye response. 5. No dye response which corresponded to the change of redox level of cytochrome b was observed in the titration curve. Addition of antimycin A slightly decreased the dye response. 6. The dye response was decreased under phosphorylating conditions. 7. From the results obtained localization of the electron transfer components in chromatophore membrane is discussed.