title: Photo-reduction of flavin mononucleotide to semiquinone form in LOV domain mutants of blue-light receptor phot from Chlamydomonas reinhardtii.
abstract: The photo-excitation dynamics of the mutants LOV1-C57S and LOV2-C250S of the LOV-domains of the phototropin photoreceptor phot from the green alga Chlamydomonas reinhardtii is investigated by absorption and fluorescence studies. The LOV domains fused to a maltose binding protein (MBP) are expressed in Escherichia coli. The mutants were studied under aerobic conditions in aqueous solution at pH 8. Blue-light exposure reduced the fully oxidized flavin mononucleotide, FMN(ox), to FMN semiquinone, FMNH*, (quantum efficiency around 1%) which further reduced to FMN hydroquinone, FMN(red)H(2) or FMN(red)H(-) (quantum efficiency ca. 3 x 10(-5)). In the dark both reduced forms recovered back to the oxidized form on a minute timescale. Besides photoreduction, blue-light photo-excitation of the mutants resulted in photoproduct formation (efficiency in the 2 x 10(-4) - 10(-3) range). Photo-reaction schemes for the mutants are discussed.
authors.affiliation: Institut für Physikalische und Theoretische Chemie, Universität Regensburg, D-93053 Regensburg, Germany.
authors.forename: S-H
authors.initials: SH
authors.lastname: Song
authors.forename: B
authors.initials: B
authors.lastname: Dick
authors.forename: A
authors.initials: A
authors.lastname: Penzkofer
authors.forename: P
authors.initials: P
authors.lastname: Hegemann
mesh_terms: D000818:Animals; D016227:Benzoquinones / Q000032:analysis* / Q000528:radiation effects; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000528:radiation effects*; D005486:Flavin Mononucleotide / Q000378:metabolism / Q000528:radiation effects*; D009154:Mutation; D010084:Oxidation-Reduction
chemical_list: D016227:Benzoquinones; C025232:semiquinone radicals; D005486:Flavin Mononucleotide