title: Correlation of paramagnetic states and molecular structure in bacterial photosynthetic reaction centers: the symmetry of the primary electron donor in Rhodopseudomonas viridis and Rhodobacter sphaeroides R-26.
abstract: The orientation of the principal axes of the primary electron donor triplet state measured in single crystals of photosynthetic reaction centers is compared to the x-ray structures of the bacteria Rhodobacter (Rb.) sphaeroides R-26 and Rhodopseudomonas (Rps.) viridis. The primary donor of Rps. viridis is significantly different from that of Rb. sphaeroides. The measured directions of the axes indicate that triplet excitation is almost completely localized on the L-subunit half of the dimer in Rps. viridis but is more symmetrically distributed (approximately 63% on the L half of the special pair and approximately 37% on the M half) on the dimeric donor in Rb. sphaeroides R-26. The large reduction of the zero field splitting parameters relative to monomeric bacteriochlorophyll triplet in vitro suggests significant participation of asymmetrical charge transfer electronic configurations in the special pair triplet state of both organisms (approximately 23% in Rps. viridis and approximately 13% in Rb. sphaeroides).
authors.affiliation: Chemistry Division, Argonne National Laboratory, IL 60439.
authors.forename: J R
authors.initials: JR
authors.lastname: Norris
authors.forename: D E
authors.initials: DE
authors.lastname: Budil
authors.forename: P
authors.initials: P
authors.lastname: Gast
authors.forename: C H
authors.initials: CH
authors.lastname: Chang
authors.forename: O
authors.initials: O
authors.lastname: el-Kabbani
authors.forename: M
authors.initials: M
authors.lastname: Schiffer
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D045342:Light-Harvesting Protein Complexes; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D012241:Rhodopseudomonas / Q000378:metabolism*; D013045:Species Specificity
chemical_list: D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins