[Photoreduction of bacteriophenophytin b in the primary light reaction of Rhodopseudomonas viridis chromatophores].

Photoconversions of the reaction center pigments in chromatophores of nonsulfur purple bacteria Rhodopseudomonas viridis have been studied as a function of redox potential of medium (Eh). It has been shown that at a decrease in the Eh values from +400 mV to--100 divided by--600 mV a photo-induced accumulation of P980+ (oxidized primary electron donor in R. viridis) is replaced by the photoaccumulation of a reduced pigment complex P800 (bleaching of bacteriopheophytin b absorption bands at 545 and 800 nm, a development of broad bands at 680 and 430 nm and a blue shift of the bacteriochlorophyll band at 830 nm). The P800 photoreduction is observed under illumination by light with lambda greater than 900 nm between +20 divided by--196 degrees C at pH 3,5--12,5 and is accompanied by oxidation of the cytochrome and an increase in fluorescence yield of bacteriochlorophyll. It is suggested that P800 accepts an electron from the P980 in the primary photoreaction, which preceeds ubiquinone reduction. A midpoint redox potential (Em) is found to be of --620(+/- 20) mV for the P800/P800- and +515 (+/-20) mV for the P980/+P980. At a decrease in the Eh value down to -400 mV luminescence has been detected with T1/2 8 nsec, an activation energy of 0,065 +/- 0,02 ev and quantum yield being close to the fluorescence yield. It is assumed that this luminescence is a result of charge recombination in the biradical P980+ -- P800-.