Titles of related papers in other sections

(i) Purified bovine heart mitochondrial cytochrome b-c₁ complex (ubiquinone-cytochrome c oxidoreductase) and photosynthetic reaction centres isolated from Rhodopseudomonas sphaeroides strain R-26 have been incorporated into lipid vesicles. In the presence of cytochrome c and ubiquinone-2, light activation caused a cyclic electron transfer involving both components. (2) Since cytochrome c is added outside the vesicles, it is both reduced by the cytochrome b-c₁ complex and oxidised by the reaction centre on the outside of the vesicles. Ubiquinone-2, however, is reduced by the reaction centres at a site in contact with the inside of the vesicles, but the reduced form, ubiquinol-2, is oxidised by the cytochrome b-c₁ complex at a site in contact with the outer aqueous phase. (3) In the presence of valinomycin plus K⁺, initiation of cyclic electron flow causes protons to move from inside the vesicles to the outer medium and the $\text{H}{}^{\mathrm{+}}\text{2}\text{e}{}^{\mathrm{?}}$ ratio was calculated to be close to 4.