OXIDATION-REDUCTION AND EPR PROPERTIES OF A CYTOCHROME COMPLEX FROM Chromatium vinosum

A cytochrome b₅₆₀-c₅₅₃ containing fraction from the photosynthetic purple sulfur bacterium Chromatium vinosum has been shown to contain equimolar amounts of the two cytochromes and also to contain ubiquinone. The oxidation-reduction midpoints (at pH 7.5) of cytochrome b₅₆₀ and c₅₅₃ in this fraction are −5 and +20 mV, respectively, essentially identical to the values found for the cytochromes in chromatophores. The fully oxidized fraction exhibits EPR features at g = 2.93 and 3.35. The former had previously been identified as originating from ferricytochrome c₅₅₃, while the latter appears to arise from ferricytochrome b_S60.