title: Effect of oxygen on temporary stabilization of photoreduced quinone acceptors in Rhodobacter sphaeroides reaction centers.
abstract: The effect of molecular oxygen on the photochemical activity of the Rhodobacter sphaeroides reaction centers frozen to 160 K under actinic illumination was investigated by the ESR method. About 90% of initially photochemically active bacteriochlorophyll (P) were fixed at 160 K for a long time in aerobic samples in an inactive form. In anaerobic samples, not more than 65% were fixed in an inactive form under the same conditions. In aerobic preparations, a small portion of photochemically active bacteriochlorophyll (about 10%) that retains its photochemical activity at 160 K after freezing under illumination has dark reduction kinetics similar to that of samples at room temperature after several seconds of actinic illumination. In anaerobic samples frozen under illumination, the remaining photochemically active reaction centers (35%) have the same dark reduction kinetics as samples illuminated at 295 K for 1-2 min. The conclusion is that the irreversible stabilization of bacteriochlorophyll P in the oxidized inactive state formed in the reaction centers frozen under illumination is brought about by light-induced conformational changes fixed under low temperatures.
authors.affiliation: Faculty of Biology, Lomonosov Moscow State University, Moscow 119899, Russia. knox@biophys.msu.ru
authors.forename: P P
authors.initials: PP
authors.lastname: Knox
authors.forename: M
authors.initials: M
authors.lastname: Heinnickel
authors.forename: A B
authors.initials: AB
authors.lastname: Rubin
mesh_terms: D020130:Bacterial Chromatophores / Q000201:enzymology*; D001429:Bacteriochlorophylls / Q000737:chemistry*; D002455:Cell Division; D005615:Freezing; D007700:Kinetics; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D010777:Photochemistry; D011809:Quinones / Q000737:chemistry*; D012242:Rhodobacter sphaeroides / Q000201:enzymology*; D013053:Spectrophotometry
chemical_list: D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D011809:Quinones; D010100:Oxygen