title: Localization of reaction center and B800-850 antenna pigment proteins in membranes of Rhodobacter sphaeroides.
abstract: The localization of the N- and C-terminal regions of pigment-binding polypeptides of the bacterial photosynthetic apparatus of Rhodobacter sphaeroides was investigated by proteinase K treatment of chromatophore and spheroplast-derived vesicles and amino acid sequence determination. Under conditions of proteinase K treatment of chromatophores, which left the in vivo absorption spectrum and the membrane intact, 15 and 46 amino acyl residues from the N-terminal regions of the L and M subunits, respectively, of the reaction center polypeptides were removed. The N termini are therefore exposed on the cytoplasmic surface of the membrane. The C-terminal domain of the light-harvesting B800-850 alpha and B870 alpha polypeptides was found to be exposed on the periplasmic surface of the membrane. A total of 9 and 13 amino acyl residues were cleaved from the B800-850 alpha and B870 alpha polypeptides, respectively, when spheroplasts were treated with proteinase K. The N-terminal regions of the alpha polypeptides were not digested in either membrane preparation and were apparently protected from proteolytic attack. Seven N-terminal amino acyl residues of the B800-850 beta polypeptide were removed after the digestion of chromatophores. C-terminal residues were not removed after the digestion of chromatophores or spheroplasts. The C termini seem to be protected from protease attack by interaction with the membrane. Therefore, the N-terminal regions of the beta polypeptides are exposed on the cytoplasmic membrane surface. The C termini of the beta polypeptides are believed to point to the periplasmic space.
authors.affiliation: European Molecular Biology Laboratory, Heidelberg, Federal Republic of Germany.
authors.forename: M H
authors.initials: MH
authors.lastname: Tadros
authors.forename: R
authors.initials: R
authors.lastname: Frank
authors.forename: J Y
authors.initials: JY
authors.lastname: Takemoto
authors.forename: G
authors.initials: G
authors.lastname: Drews
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000032:analysis*; D019286:Endopeptidase K; D008565:Membrane Proteins / Q000032:analysis; D008566:Membranes / Q000032:analysis; D045322:Photosynthetic Reaction Center Complex Proteins; D012244:Rhodospirillaceae / Q000032:analysis*; D012697:Serine Endopeptidases / Q000378:metabolism; D013053:Spectrophotometry
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; D012697:Serine Endopeptidases; D019286:Endopeptidase K