LOW POTENTIAL TITRATION OF FLUORESCENCE YIELD CHANGES IN PHOTOSYNTHETIC BACTERIA

The fluorescence yield of whole cells of the photosynthetic bacteria Chromatium, Rhodospirillum rubrum, and Rhodopseudomonas spheroides was measured in low intensity light as a function of redox potential under anaerobic conditions at pH 8.0. The titration curves were fit by the Nernst equation for a one-electron reaction. The midpoint potentials were -160 mV and -145 mV, respectively, for Chromatium and R. rubrum. The R. spheroides showed less reversibility and is characterized by midpoints of -65 mV and -90 mV for the oxidative and reductive titrations. © 1969.