title: Energy trapping and detrapping in reaction center mutants from Rhodobacter sphaeroides.
abstract: Time-resolved fluorescence of chromatophores isolated from strains of Rhodobacter sphaeroides containing light harvesting complex I (LHI) and reaction center (RC) (no light harvesting complex II) was measured at several temperatures between 295 K and 10 K. Measurements were performed to investigate energy trapping from LHI to the RC in RC mutants that have a P/P(+) midpoint potential either above or below wild-type (WT). Six different strains were investigated: WT + LHI, four mutants with altered RC P/P(+) midpoint potentials, and an LHI-only strain. In the mutants with the highest P/P(+) midpoint potentials, the electron transfer rate decreases significantly, and at low temperatures it is possible to directly observe energy transfer from LHI to the RC by detecting the fluorescence kinetics from both complexes. In all mutants, fluorescence kinetics are multiexponential. To explain this, RC + LHI fluorescence kinetics were analyzed using target analysis in which specific kinetic models were compared. The kinetics at all temperatures can be well described with a model which accounts for the energy transfer between LHI and the RC and also includes the relaxation of the charge separated state P(+)H(A)(-), created in the RC as a result of the primary charge separation.
authors.affiliation: Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287-1604, USA. zivile@asu.edu
authors.forename: Zivile
authors.initials: Z
authors.lastname: Katiliene
authors.forename: Evaldas
authors.initials: E
authors.lastname: Katilius
authors.forename: Neal W
authors.initials: NW
authors.lastname: Woodbury
mesh_terms: D002462:Cell Membrane / Q000737:chemistry / Q000502:physiology / Q000528:radiation effects; D004579:Electron Transport; D004735:Energy Transfer / Q000502:physiology*; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects*; D009154:Mutation; D045331:Photosystem I Protein Complex / Q000737:chemistry / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects; D015203:Reproducibility of Results; D012242:Rhodobacter sphaeroides / Q000737:chemistry / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects*; D012680:Sensitivity and Specificity; D013696:Temperature
chemical_list: D045342:Light-Harvesting Protein Complexes; D045331:Photosystem I Protein Complex; D011994:Recombinant Proteins