Ubiquinone concentrations in athiorhodaceae grown under various environmental conditions.

1. The nature and concentration of ubiquinone in six species of Athiorhodaceae have been examined after growth under aerobic and photosynthetic conditions. 2. Increase in ubiquinone concentration during adaptive synthesis of photosynthetic pigments by Rhodopseudomonas spheroides incubated under low-aeration conditions was observed. 3. The nature of the carbon source was found to have a marked effect on ubiquinone, as well as bacteriochlorophyll, concentrations.