title: Interaction of cytochrome c with reaction centers of Rhodopseudomonas sphaeroides R-26: localization of the binding site by chemical cross-linking and immunochemical studies.
abstract: The location of the cytochrome binding site on the reaction center of Rhodopseudomonas sphaeroides was studied by two different approaches. In one, cross-linking agents, principally dithiobis(propionimidate) and dimethyl suberimidate, were used to link cytochrome c and cytochrome c2 to reaction centers; in the other, the inhibition of electron transfer by antibodies against the subunits was investigated. Cytochrome c (horse) cross-linked to the L and M subunits, whereas cytochrome c2 (R. sphaeroides) cross-linked only to the L subunit. The cross-linked reaction center-cytochrome complexes were isolated by affinity chromatography. The rate of electron transfer in the cross-linked cytochrome c2 complex was the same as that in the un-cross-linked complex. However, when cytochrome c was used, the rate in the cross-linked complex was about 15 times slower than that in the un-cross-linked complex. Fab fragments of antibodies specific against the L and M subunits blocked electron transfer from both cytochrome c (horse) and cytochrome c2 (R. sphaeroides). Antibodies specific for the H subunit did not block either reaction. We conclude that the cytochrome binding site on the reaction center is close (approximately 10 A) to both the L and M subunits, possibly in a cleft between them.
mesh_terms: D001665:Binding Sites; D003432:Cross-Linking Reagents; D003574:Cytochrome c Group / Q000276:immunology / Q000378:metabolism*; D045362:Cytochromes c2; D004119:Dimethyl Adipimidate; D004120:Dimethyl Suberimidate; D004579:Electron Transport; D004591:Electrophoresis, Polyacrylamide Gel; D007096:Imidoesters; D007140:Immunoglobulin Fab Fragments; D007158:Immunologic Techniques; D007700:Kinetics; D010777:Photochemistry; D012242:Rhodobacter sphaeroides / Q000378:metabolism*
chemical_list: D003432:Cross-Linking Reagents; D003574:Cytochrome c Group; D007096:Imidoesters; D007140:Immunoglobulin Fab Fragments; C024244:dithiobispropionimidate; D004119:Dimethyl Adipimidate; D004120:Dimethyl Suberimidate; D045362:Cytochromes c2