Isolation of cytochrome bc₁ complexes from the photosynthetic bacteria Rhodopseudomonas viridis and Rhodospirillum rubrum

Cytochrome bc₁ complexes have been isolated from wild type Rhodopseudomonas viridis and Rhodospirillum rubrum and purified by affinity chromatography on cytochrome c-Sepharose 4B. Both complexes are largely free of bacteriochlorophyll and carotenoids and contain cytochromes b and c₁ in a 2:1 molar ratio. For the Rps. viridis complex, evidence has been obtained for two spectrally distinct b-cytochromes. The R. rubrum complex contains a Rieske iron-sulfur protein (present in approximately 1:1 molar ratio to cytochrome c₁) and catalyzes an antimycin A- and myxothiazol-sensitive electron transfer from duroquinol to equine cytochrome c or R. rubrum cytochrome c₂. Although an attempt to prepare a cytochrome bc₁ complex from the gliding green bacterium Chloroflexus aurantiacus was not successful, membranes isolated from phototrophically grown Cfl. aurantiacus were shown to contain a Rieske iron-sulfur protein and protoheme (the prosthetic group of b-type cytochromes).