Location of the Electron Accepting Site of a b-Type Cytochrome Oxidase in Purified Chromatophore Membranes and Spheroplast Membrane Vesicles from Photosynthetically Grown Rhodopseudomonas sphaeroides

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Purified chromatophore membranes and spheroplast membrane vesicles were prepared from Rhodopseudomonas sphaeroides by the method of Michels and Konings (1978). The cytochrome c oxidase activity of the spheroplast membrane vesicles was about 15-fold higher on a bacteriochlorophyll basis than that of the chromatophore membranes. The cytochrome c oxidase activity of the chromatophore membranes was greatly stimulated (about 10-fold) by an addition of Triton X-100 (0.1%). but there was less stimulated (about 1.5-fold) in the case of spheroplasts. The pH optimum of the oxidase activities of the spheroplast membrane vesicles and of chromatophore membranes treated with 0.1% Triton X-100, and the salt dependencies of the activity of both preparations were the same. These results show that the membrane-bound b-type cytochrome oxidase of this bacterium accepts electrons from ferrocytochrome c on the periplasmic side of the membrane (on the outer surface of the spheroplast membrane vesicles). These results also are consistent with the fact that cytochrome c_2 is located in the periplasmic space in this bacterium.
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