title: First steps in the phytochrome phototransformation: a comparative femtosecond study on the forward (Pr --> Pfr) and back reaction (Pfr --> Pr).
abstract: The primary light-induced events in the reversible Pr right harpoon over left harpoon Pfr phototransformation are investigated by femtosecond absorption spectroscopy using a pump-probe technique. After the selective electronic excitation of Pr and Pfr with pulses at 610 and 730 nm, respectively, the transient absorption spectra were measured as a function of the delay time and subjected to a global fit analysis. As a result of this analysis, the decay-associated spectra of the kinetic components involved in the formation of the first photoproducts in the forward and back reaction are obtained. These spectra provide a more detailed understanding of the primary stages in the light-induced transformations. In addition, the influence of the solvent viscosity on the initial reaction steps was studied. In each direction of reaction, a short-lifetime component is found to be strongly viscosity-dependent, indicating that the primary photochemistry encompasses intramolecular motions of the chromophore or its proximal amino acid side chains. H-D exchange has no significant effect on the kinetics of the initial photoprocesses. This suggests that the isomerization reaction in both directions is not accompanied by a rate-limiting proton transfer.
authors.affiliation: Institute for Optics and Quantumelectronics, Friedrich-Schiller-University, Max-Wien-Platz 1, D-07743 Jena, USA.
authors.forename: M
authors.initials: M
authors.lastname: Bischoff
authors.forename: G
authors.initials: G
authors.lastname: Hermann
authors.forename: S
authors.initials: S
authors.lastname: Rentsch
authors.forename: D
authors.initials: D
authors.lastname: Strehlow
mesh_terms: D018554:Avena / Q000737:chemistry; D003903:Deuterium; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D007834:Lasers; D008027:Light; D010782:Photolysis; D010834:Phytochrome / Q000737:chemistry*; D011522:Protons; D013056:Spectrophotometry, Ultraviolet; D013057:Spectrum Analysis / Q000379:methods; D013995:Time
chemical_list: D011522:Protons; D010834:Phytochrome; D003903:Deuterium