Fast Stages of Photoelectric Processes in Biological Membranes

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Abstract
Chromatophores of photosynthetic bacteria Rhodospirillum rubrum, Rhodopseudomonas sphaeroides and Chromatium minutissimum were associated with a collodion film impregnated with a decane solution of asolectin. A very short light flash inducing a single turnover of the chromatophore photosynthetic redox system induced the formation of an electric potential difference amounting to 60 mV, directed across the film as measured with an orthodox electrometer technique. The main phase of the photoelectric response had a .tau. value of < 200 ns. Addition of menadione and some other redox mediators increases the main phase amplitude and induces a slower phase (.tau. = 200 .mu.s). In C. minutissimum chromatophores that retained their endogeneous cytochrome c pool, one more electrogenic phase was revealed (.tau. = 20 .mu.s). Redox titrations of the electric response and bacteriochlorophyll absorption at 430 nm as well as measurements of the kinetics of cytochrome c oxidation have indicated that the fastest electrogenic phase is due to electron transfer from bacteriochlorophyll to Fe-ubiquinone, the 20-.mu.s phase to cytochrome c2+-bacteriochlorophyll+ oxidoreduction, and the 200-.mu.s phase to Fe-ubiquinone- oxidation by a secondary quinone. In the decay of the photoelectric response, a 30-ms phase was identified which was explained by a reverse electron transfer from reduced Fe-ubiquinone to oxidited bacteriochlorophyll. The difference in the fast kinetics of photoelectric generation by the bacteriochlorophyll system from those by bacterial and animal rhodopsins was discussed.

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