Light stimulation of the respiratory activity of Rhodospirillum rubrum chromatophores

Respiratory activity of chromatophores of Rhodospirillum rubrum, as measured by the O₂ uptake, was almost doubled by illumination. Succinoxidase activity of chromatophores was inhibited considerably by o-phenanthroline but not inhibited by KCN either in the dark or light. The aerobic oxidation of p-phenylenediamine in the dark was not inhibited by o-phenanthroline but was completely inhibited by KCN, whereas the oxidation in the light was sensitive to o-phenanthroline but insensitive to KCN. o-Phenanthroline also inhibited other CN⁻-insensitive reactions in chromatophores, such as photooxidation of reduced cytochrome c₂ and the dark-anaerobic oxidation of NADH coupled to the reduction of fumarate. Antimycin A did not inhibit the succinoxidase activity in the dark, but significantly inhibited the activity in the light. Succinate-cytochrome c₂ reductase activity was sensitive to antimycin A but insensitive to o-phenanthroline, whereas NADH-cytochrome c₂ reductase activity was insensitive to antimycin A but sensitive to o-phenanthroline.

The terminal oxidation system in chromatophores is discussed with particular reference to the marked stimulation of O₂ uptake by illumination.