title: Transverse membrane topography of the B875 light-harvesting polypeptides of wild-type Rhodobacter sphaeroides.
abstract: Purified B875 light-harvesting complex, chromatophores, and spheroplast-derived vesicles from wild-type Rhodobacter sphaeroides were treated with proteinase K or trypsin, and the alpha and beta polypeptides were analyzed by electrophoretic, immunochemical, and protein-sequencing methods. With the purified complex, proteinase K digested both polypeptides and completely eliminated the A875 peak. Trypsin digested the alpha polypeptide and reduced the A875 by 50%. Proteinase K cleaved the beta polypeptide of chromatophores and the alpha polypeptide of spheroplast-derived vesicles. Sequence analyses of polypeptides extracted from proteinase K-treated chromatophores revealed that the beta polypeptide was cleaved between amino acids 4 and 5 from the N terminus. The N terminus of the alpha polypeptide was intact. We concluded that the N terminus of the beta polypeptide is exposed on the cytoplasmic membrane surface, and the difference in the digestion patterns between the spheroplast-derived vesicles and chromatophores suggested that the C terminus of the alpha polypeptide is exposed on the periplasmic surface.
authors.affiliation: Department of Biology, Utah State University, Logan 84322-0300.
authors.forename: J Y
authors.initials: JY
authors.lastname: Takemoto
authors.forename: R L
authors.initials: RL
authors.lastname: Peterson
authors.forename: M H
authors.initials: MH
authors.lastname: Tadros
authors.forename: G
authors.initials: G
authors.lastname: Drews
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D001419:Bacteria / Q000032:analysis*; D020130:Bacterial Chromatophores / Q000032:analysis; D001426:Bacterial Proteins / Q000032:analysis*; D002462:Cell Membrane / Q000032:analysis; D002848:Chromatography, DEAE-Cellulose; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D019286:Endopeptidase K; D007118:Immunoassay; D010455:Peptides / Q000032:analysis; D045322:Photosynthetic Reaction Center Complex Proteins; D012697:Serine Endopeptidases / Q000378:metabolism; D013054:Spectrophotometry, Atomic; D014357:Trypsin / Q000378:metabolism
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D010455:Peptides; D045322:Photosynthetic Reaction Center Complex Proteins; D012697:Serine Endopeptidases; D014357:Trypsin; D019286:Endopeptidase K