Reactions of Rhodospirillum rubum extract with cytochrome c and cytochrome c2.

Observations from a number of different experimental approaches have implicated cytochrome pigments in oxidation-reduction reactions resulting from the illumination of photosynthetic tissues (l-6). Possible relationships of these cytochromes to those of the respiratory chain pigments which react with oxygen in the dark have been considered. Vernon (7) isolated a soluble cytochrome in good yield from the photosynthetic bacterium Rfwdospirillum rubrum. This pigment, which has been designated cytochrome c2 (8), has absorption spectrum properties nearly identical with those of mammalian cytochrome c, but the oxidation-reduction potential resembles that of the cytochrome f found in the chloroplasts of green plant tissues. Vernon and Kamen (3,4) studied the oxidation of mammalian cytochrome c and the bacterial cytochrome c2 by sonic extracts of a number of photosynthetic bacteria in the light and in the dark and concluded that all contained both a dark cytochrome c oxidase and a cytochrome c photooxidase and that the relative amounts of the two enzymes could be correlated with the relative aerobicity of the organisms. The present paper describes some properties of cell-free extracts of Rhodospirillum rubrum and further studies on the reactions of these extracts with mammalian cytochrome c and bacterial cytochrome CZ. The dark oxidation of either cytochrome was found to be very slow, and the photooxidation of the cytochrome c does not appear to be an enzymatic reaction. These two reactions cannot play significant roles in the metabolism of the bacteria.