Abstract
Photoheterotrophically grown Rhodospirillum rubrum mutant C oxidized 3,3'-diaminobenzidine (DAB) by two aerobic reactions. One reaction was light dependent. The other respiratory reaction occurred in the dark and could be inhibited by 0.1 M KCN. DAB was not oxidized under anaerobic conditions. Cytochemical results, obtained by reacting viable cells with DAB, indicated that the two reactions were associated with different regions of the cellular membrane system. Under dark conditions, oxidized DAB was deposited along the cytoplasmic membrane. In the light, the cytochemical reagent accumulated at both the cytoplasmic and the intracytoplasmic photosynthetic membranes. DAB oxidation activity was measured by sensitive spectrophotometric and polarographic techniques. Under 880 nm actinic illumination, the rate of DAB oxidation was about 5.5-fold faster than in the dark. Determination of O2 consumption associated with the two DAB oxidation reactions showed that white light stimulated the rate of O2 uptake by about the same extent.