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[1] Study of photosynthetic electron transport by redox probing electron transport in purple non-sulfur bacteria / A. Y. MULKIDZHANYAN, M. I. VERKHOVSKII, V. P. SHINKAREV et al. // Biokhimiya. — 1985. — Vol. 50, no. 11. — P. 1786–1796. The oxidation of redox mediators-N,N,N'N'-tetramethylparaphenylenediamine (TMPD), 2,3,5,6-tetramethylparaphenylenediamine (DAD), phenazinemethosulfate (FMS) and variamine blue-induced by light flashes was studied in chromatophore suspensions prepared from the purple non-sulphur bacteria Rhodopseudomonas sphaeroides and Rhodospirillum rubrum. Redox conversions of the mediators were recorded spectrophotometrically and potentiometrically by the photo-induced changes in redox potential values. It was found that in Rps. sphaeroides chromatophores illuminated by an even number of light flashes the degree of mediator oxidation is much higher than in those illuminated with an odd number of light flashes. This effect is not coupled with the nature of the mediator and is due to the formation of ubiquinol molecules in the acceptor part of the photosynthetic reaction center (PRC) after illumination with an even number of light flashes. These molecules are oxidized by ubiquinol: cytochrome c2-oxidoreductase and thus reduce the photooxidized carriers on the donor side of PRC faster than the mediator. Under these conditions, only one of the two electrons liberated via oxidation of ubiquinol molecules formed in the acceptor site of PRC are returned to the donor part of PRC, while the other one enters an electron-dense area, presumably a ubiquinone pool. Studies on effects of various electron transport inhibitors (o-phenanthroline, antimycin A, myxothiazol, mucidin, N,N'-dicyclohexylcarbodiimide) on photo-induced redox conversions of TMPD in Rps. sphaeroides chromatophores revealed that the changes in the type of photoresponses depend on the nature of quinone-binding sites of the electron transport chain responsible for the inhibitor blocking. The experimental results are interpreted within the framework of the Mitchell's Q-cycle.

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