Isolation and spectral characteristics of the photochemical reaction center of Rhodopseudomonas viridis.

A method is described for isolation of the Rhodopseudomonas viridis reaction center complex free of altered, 685 nm absorbing pigment. This improved preparation contains two c-type cytochromes in the ratio P-960: cytochrome c-558: cytochrome c-553 of 1:2:2 to 3. The near infrared spectral forms of the reduced preparation are located at 790, 832, 846, and 987 nm at 77 K; the oxidized complex absorbs at 790, 808, 829 and approx. 1310 nm. The 790 nm band is attributed to bacteriophaeophytin b and the other absorbances to bacteriochlorophyll b, The visible absorption bands may be assigned to these pigments and to the cytochromes present and, probably to a carotenoid. The presence of two bacteriochlorophyll b spectral forms in the P+-830 band suggests that exciton interactions occur among pigments in the oxidized, as well as the reduced, reaction center. Changes in the 790 and 544 nm bands upon illumination of the reaction center preparation at low redox potential may be indicative of a role for bacteriophaeophytin b in primary photochemical events.