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 ofChromatium under various experimental conditions were measuredby extracting the ubiquinone with organic solvents. Under aerobicconditions, 80% and 75% of the total ubiquinone in Chromatiumexisted in the oxidized form in the dark and in the light, respectively.On illumination in the presence of thiosulfate under aerobicconditions, about 15% of the total ubiquinone was photoreduced.In the presence of KGN under aerobic conditions, about 50% and60% of the total ubiquinone existed in the oxidized form inthe dark and in the light, respectively. Under anaerobic conditions, about 25% and 75% of the total ubiquinoneexisted in the oxidized form in the dark and in the light, respectively.This light-induced oxidation of ubiquinone under anaerobic conditionswas inhibited by piericidin A. These findings are in accordancewith previous findings from spectroscopic experiments. (Received November 11, 1968; )