Studies on light-induced inhibition of respiration in purple bacteria: Action spectra for Rhodospirillum rubrum and Rhodopseudomonas spheroides

1. 1. A reversible light-induced inhibition of respiration has been studied in the purple bacteria Rhodospirillum rubrum and Rhodopseudomonas spheroides by measuring O2 uptake with a Teflon-covered Pt electrode. The action spectra follow the absorption of bacteriochlorophyll and show a partial participation of carotenoids which was higher in Rhodopseudomonas than in Rhodospirillum. 2. 2. Light saturation of the inhibition effect occurs at a much lower light intensity than saturation of photosynthesis. Respiration stimulation after the end of illumination, similar to that occurring in red algae, could be observed. The mesurements suggest an intimate coupling between photosynthesis and respiration. The inhibition effect seems to be brought about by a competition for electrons (or H+) by intermediates common to both processes. 3. 3. N-Methylphenazonium methosulfate stimulates dark O2 uptake and inhibits the light suppression of respiration