Light-induced reactions of ubiquinone in photosynthetic bacterium, Chromatium D III. Oxidation-reduction state of ubiquinone in intact cells of Chromatium D.

Oxidation-reduction levels of ubiquinone in intact cells of Chromatium under various experimental conditions were measured by extracting the ubiquinone with organic solvents. Under aerobic conditions, 80% and 75% of the total ubiquinone in Chromatium existed in the oxidized form in the dark and in the light, respectively. On illumination in the presence of thiosulfate under aerobic conditions, about 15% of the total ubiquinone was photoreduced. In the presence of KGN under aerobic conditions, about 50% and 60% of the total ubiquinone existed in the oxidized form in the dark and in the light, respectively. Under anaerobic conditions, about 25% and 75% of the total ubiquinone existed in the oxidized form in the dark and in the light, respectively. This light-induced oxidation of ubiquinone under anaerobic conditions was inhibited by piericidin A. These findings are in accordance with previous findings from spectroscopic experiments.