title: Ultrafast pump-probe spectroscopy of native etiolated oat phytochrome.
abstract: Absorption difference profiles were obtained at wavelengths from 640 to 700 nm with 1-2-ps resolution in a study of primary photoprocesses in the Pr-->Pfr transformation in native oat phytochrome. These experiments were performed using low-intensity laser pulses at high repetition rate; fast sample recycling ensured that essentially all phytochrome species were excited from the Pr ground state. The Pr*-stimulated emission decay at wavelengths > 670 nm exhibits major components with lifetimes of approximately 16 and 50-60 ps. Formation of the asymptotic 695-nm lumi-R absorption spectrum rapidly follows stimulated emission decay. Photoexcitation of one or both of the lumi-R intermediates instantaneously recreates fluorescing Pr* phytochrome, which is spectroscopically and kinetically indistinguishable from that generated by direct illumination of ground-state Pr. This is consistent with assignment of lumi-R as a species in which the chromophore has isomerized from the Z,Z,Z to the Z,Z,E conformation. Anisotropy studies indicate that the orientations of the Pr and lumi-R absorption transition moments are nearly parallel, since little anisotropy decay occurs during the 500-ps time window of these experiments.
authors.affiliation: Department of Chemistry and Ames Laboratory-USDOE, Iowa State University, Ames 50011.
authors.forename: S
authors.initials: S
authors.lastname: Savikhin
authors.forename: T
authors.initials: T
authors.lastname: Wells
authors.forename: P S
authors.initials: PS
authors.lastname: Song
authors.forename: W S
authors.initials: WS
authors.lastname: Struve
mesh_terms: D002523:Edible Grain / Q000737:chemistry*; D005454:Fluorescence Polarization; D007834:Lasers; D010834:Phytochrome / Q000737:chemistry*; D013057:Spectrum Analysis
chemical_list: D010834:Phytochrome