title: Membrane topography of the photosynthetic reaction center polypeptides of Rhodopseudomonas sphaeroides.
abstract: The topography of the photosynthetic reaction center (RC) polypeptides (H, M, and L) was investigated by proteolysis and radioiodination of membrane vesicles isolated from Rhodopseudomonas sphaeroides. Chromatophores, obtained from French-pressed cell lysates, are closed vesicles' and oriented inside out with respect to the cytoplasmic membrane (cytoplasmic side out). Spheroplast-derived vesicles (SDVs), obtained after osmotic lysis of lysozyme-treated cells, are oriented right side in (periplasmic side out). Alpha-Chymotrypsin treatment of chromatophores and trypsin treatment of SDVs resulted in cleavage of H. Alpha-Chymotrypsin treatment of SDVs did not cleave H, and trypsin treatment of chromatophores did not consistently cleave this polypeptide. M and L of both vesicles were apparently not affected by these proteases. The SDV trypsin cleavage product of H was identified by alpha-chymotryptic (125)I-labeled peptide mapping and had a molecular weight of 26 000. Membrane surface radioiodination with chloroglycoluril coated on glass tubes resulted in preferential labeling of H and M of SDVs and chromatophores. The radiospecific activities of H, M, and L were higher with labeling of SDVs as compared to labeling of chromatophores. Alpha-Chymotryptic (125)I-labeled peptide maps of H, M, and L from surface-radioiodinated SDVs differed from the corresponding maps of these polypeptides from surface-radioiodinated chromatophores. The results indicate the asymmetric exposure of H, M, and L on opposite surfaces of the R. sphaeroides membrane. Exposed iodination sites of these polypeptides are more abundant on the periplasmic surface than on the cytoplasmic surface of this membrane.
mesh_terms: D001426:Bacterial Proteins / Q000302:isolation & purification / Q000378:metabolism*; D002918:Chymotrypsin; D007700:Kinetics; D010446:Peptide Fragments / Q000032:analysis; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins; D011487:Protein Conformation; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D014357:Trypsin
chemical_list: D001426:Bacterial Proteins; D010446:Peptide Fragments; D045322:Photosynthetic Reaction Center Complex Proteins; D002918:Chymotrypsin; D014357:Trypsin