Figure 2.

Biochemical characterization of the oligomeric state of the cyt b₆f complex isolated from F. diplosiphon SF33. (A) Sucrose density gradient profile of the cyt b₆f complex from F. diplosiphon SF33 eluted from a Ni affinity chromatography column, showing the presence of the monomer and dimer. (B) Native gel electrophoresis of the purified cyt b₆f complex dimer (Fd-dimer) and monomer (Fd-monomer) from F. diplosiphon SF33. Purified cyt b₆f from spinach (Sp-dimer), Synechocystis PCC 6803 (Syn-monomer), and Nostoc PCC 7120 (Nos-dimer) were used as controls for comparison. Molecular mass standards (MW, in kilodaltons) are also shown (lane 1). (C) Subunit composition of the cyt b₆f complex analyzed by SDS–PAGE. F. diplosiphon SF33 dimer (Fd-dimer) and monomer (Fd-monomer) show prominent bands corresponding to three large subunits, i.e., cyt f, cyt b₆, and subIV. The band corresponding to ISP was comparatively faint. Purified dimeric cyt b₆f from spinach (Sp-dimer) was used as a standard for comparison. Molecular mass standards (MW, kilodaltons) are shown. (D) Densitometry profile of the four large cyt b₆f subunits from spinach (Sp-dimer, lane 1) and F. diplosiphon SF33 dimer (Fd-dimer, lane 2). Cyt f, cyt b₆, ISP, and subIV are labeled 1–4, respectively. The corresponding lane profiles are shown adjacent to the gel image. (E) Two-dimensional CN-PAGE of the cyt b₆f dimer from F. diplosiphon SF33. Ten micrograms of the protein was resolved via 4 to 12% CN-PAGE in the first dimension followed by 12% SDS–PAGE in the second dimension. The gel was Coomassie-stained for visualization. Protein spots corresponding to cyt f, cyt b₆, and subIV are visible. For reference, molecular mass standards (MW, kilodaltons) are shown in the left-most lane, and spinach cyt b₆f is shown in the right-most lane.