title: Investigation of B-branch electron transfer by femtosecond time resolved spectroscopy in a Rhodobacter sphaeroides reaction centre that lacks the Q(A) ubiquinone.
abstract: The dynamics of electron transfer in a membrane-bound Rhodobacter sphaeroides reaction centre containing a combination of four mutations were investigated by transient absorption spectroscopy. The reaction centre, named WAAH, has a mutation that causes the reaction centre to assemble without a Q(A) ubiquinone (Ala M260 to Trp), a mutation that causes the replacement of the H(A) bacteriopheophytin with a bacteriochlorophyll (Leu M214 to His) and two mutations that remove acidic groups close to the Q(B) ubiquinone (Glu L212 to Ala and Asp L213 to Ala). Previous work has shown that the Q(B) ubiquinone is reduced by electron transfer along the so-called inactive cofactor branch (B-branch) in the WAAH reaction centre (M.C. Wakeham, M.G. Goodwin, C. McKibbin, M.R. Jones, Photo-accumulation of the P(+)Q(B)(-) radical pair state in purple bacterial reaction centres that lack the Q(A) ubiquinone, FEBS Letters 540 (2003) 234-240). In the present study the dynamics of electron transfer in the membrane-bound WAAH reaction centre were studied by femtosecond transient absorption spectroscopy, and the data analysed using a compartmental model. The analysis indicates that the yield of Q(B) reduction via the B-branch is approximately 8% in the WAAH reaction centre, consistent with results from millisecond time-scale kinetic spectroscopy. Possible contributions to this yield of the constituent mutations in the WAAH reaction centre and the membrane environment of the complex are discussed.
authors.affiliation: Department of Physics and Astronomy, Free University of Amsterdam, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands. dmitrij@nat.vu.nl
authors.forename: Dmitrij
authors.initials: D
authors.lastname: Frolov
authors.forename: Marion C
authors.initials: MC
authors.lastname: Wakeham
authors.forename: Elena G
authors.initials: EG
authors.lastname: Andrizhiyevskaya
authors.forename: Michael R
authors.initials: MR
authors.lastname: Jones
authors.forename: Rienk
authors.initials: R
authors.lastname: van Grondelle
mesh_terms: D004579:Electron Transport; D005583:Fourier Analysis; D007700:Kinetics; D008956:Models, Chemical; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012242:Rhodobacter sphaeroides / Q000737:chemistry*; D013053:Spectrophotometry / Q000379:methods*; D013997:Time Factors; D014451:Ubiquinone / Q000172:deficiency
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D014451:Ubiquinone