title: Reaction centers from Rhodopseudomonas sphaeroides in reconstituted phospholipid vesicles. I. Structural studies.
abstract: Reaction centers (RCs) from Rhodopseudomonas sphaeroides were reconstituted into asolectin vesicles by cosonication. Equilibrium centrifugation on sucrose gradients showed that the vesicles were homogeneous in density (i.e., lipid-to-protein ratio) when reconstituted at a molar lipid-to-protein ratio between 500 to 1000. At lower ratios, a considerable fraction of RCs was not incorporated into closed vesicles, while at higher ratios, an increasing population of liposomes was protein-free. The average vesicle size decreased with increasing lipid-to-protein ratio, exhibiting considerable size heterogeneity within a sample. The average diameter of the largest and smallest population of vesicles, reconstituted at a molar lipid-to-protein ratio of 560, was 1200 and 400 nm, respectively. The orientation of reconstituted RCs with respect to the plane of the membrane was determined from the flash-induced rereduction kinetics of the special-pair bacteriochlorophyll dimer in the presence of reduced cytochrome c. The predominant orientation of RCs was such that the cytochrome c binding sites faced the external medium. The net orientation of RCs in reconstituted vesicles decreased with vesicle size and was strongly influenced by the ionic strength during reconstitution.
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D003574:Cytochrome c Group / Q000378:metabolism; D045342:Light-Harvesting Protein Complexes; D008081:Liposomes; D010316:Particle Size; D045322:Photosynthetic Reaction Center Complex Proteins; D011485:Protein Binding; D011487:Protein Conformation; D012242:Rhodobacter sphaeroides / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D003574:Cytochrome c Group; D045342:Light-Harvesting Protein Complexes; D008081:Liposomes; D045322:Photosynthetic Reaction Center Complex Proteins