title: Charge separation in a reaction center incorporating bacteriochlorophyll for photoactive bacteriopheophytin.
abstract: Site-directed mutagenic replacement of M subunit Leu214 by His in the photosynthetic reaction center (RC) from Rhodobacter sphaeroides results in incorporation of a bacteriochlorophyll molecule (BChl) in place of the native bacteriopheophytin (BPh) electron acceptor. Evidence supporting this conclusion includes the ground-state absorption spectrum of the (M)L214H mutant, pigment and metal analyses, and time-resolved optical experiments. The genetically modified RC supports transmembrane charge separation from the photoexcited BChl dimer to the primary quinone through the new BChl molecule, but with a reduced quantum yield of 60 percent (compared to 100 percent in wild-type RCs). These results have important implications for the mechanism of charge separation in the RC, and rationalize the choice of (bacterio)pheophytins as electron acceptors in a variety of photosynthetic systems.
authors.affiliation: Department of Chemistry, Washington University St. Louis, MO 63130.
authors.forename: C
authors.initials: C
authors.lastname: Kirmaier
authors.forename: D
authors.initials: D
authors.lastname: Gaul
authors.forename: R
authors.initials: R
authors.lastname: DeBey
authors.forename: D
authors.initials: D
authors.lastname: Holten
authors.forename: C C
authors.initials: CC
authors.lastname: Schenck
mesh_terms: D001429:Bacteriochlorophylls / Q000378:metabolism*; D004579:Electron Transport; D006639:Histidine; D007700:Kinetics; D007930:Leucine; D045342:Light-Harvesting Protein Complexes; D016297:Mutagenesis, Site-Directed; D010674:Pheophytins / Q000378:metabolism; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000378:metabolism*; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D013053:Spectrophotometry
chemical_list: D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D010674:Pheophytins; D045322:Photosynthetic Reaction Center Complex Proteins; C006678:bacteriopheophytin; D006639:Histidine; D007930:Leucine