title: Monomeric bacteriochlorophyll is required for the triplet energy transfer between the primary donor and the carotenoid in photosynthetic bacterial reaction centers.
abstract: Reaction centers from the carotenoidless mutant Rb. sphaeroides R26 were treated with sodium borohydride which is known to remove one of the accessory monomeric bacteriochlorophylls (BB). Subsequently, the carotenoid, spheroidene, was incorporated into the modified reaction centers. It is demonstrated by optical absorption and circular dichroism experiments that spheroidene, reconstituted into the sodium borohydride-treated Rb. sphaeroides R26 reaction centers, is bound in a single site, in the same environment and with the same structure as spheroidene reconstituted into untreated (native) Rb. sphaeroides R26 reaction centers. Transient optical and electron spin resonance spectroscopic data indicate that unless the accessory BB is present, the primary donor-to-carotenoid triplet energy transfer reaction is inhibited. These observations provide direct evidence for the involvement of the accessory BB in the triplet energy transfer pathway.
authors.affiliation: Department of Chemistry, University of Connecticut, Storrs 06269.
authors.forename: H A
authors.initials: HA
authors.lastname: Frank
authors.forename: C A
authors.initials: CA
authors.lastname: Violette
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D001429:Bacteriochlorophylls / Q000378:metabolism*; D002338:Carotenoids / Q000378:metabolism*; D002734:Chlorophyll / Q000031:analogs & derivatives*; D002942:Circular Dichroism; D004578:Electron Spin Resonance Spectroscopy; D004735:Energy Transfer; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D011487:Protein Conformation; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D013053:Spectrophotometry
chemical_list: D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D002734:Chlorophyll; D002338:Carotenoids