Abstract
1. Quinone concentrations in Chlorobium thiosuphatophilum and Chloropseudomonas ethylicum have been determined under various growth conditions as a guide to their functions. 2. Three quinones were isolated from both organisms; menaquinone-7, chlorobiumquinone and a polar menaquinone, probably 1′-hydroxymenaquinone-7. 3. The concentration of chlorobiumquinone and the polar menaquinone varied in the two organisms; 87 and 2 mmoles per mole of chlorophyll respectively in C. thiosulphatophilum, and 6 and 0.6 mmoles per mole of chlorophyll in ethanol-grown Cps. ethylicum. Whereas the menaquinone-7 concentration was of the same order in the two organisms, 70 and 75 mmoles per mole of chlorophyll. 4. Resuspension of Cps. ethylicum in autotrophic medium caused a fall in the menaquinone-7 concentration to 46 mmoles per mole of chlorophyll, accompanied by increases of chlorobiumquinone and the polar menaquinone concentrations to 52 and 8 mmoles per mole of chlorophyll respectively. 5. Since chlorobiumquinone is virtually absent in ethanol-grown cells, but appears on adaptation to the sulphide medium, it is likely to be involved in the photooxidation of sulphide. Menaquinone-7 could well be involved in a cyclic phosphorylation pathway of both organisms. 6. The polar menaquinone probably is a precursor of chlorobiumquinone as its concentration is high only when the rate of chlorobiumquinone biosynthesis is high. Moreover the polar menaquinone breaks down into chlorobiumquinone in vitro.
Published Version
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