title: Spectroscopic Investigation on the Primary Photoreaction of Bathy Phytochrome Agp2-Pr of Agrobacterium fabrum: Isomerization in a pH-dependent H-bond Network.
abstract: Bathy phytochrome Agp2 from Agrobacterium fabrum exhibits an unusually low pKa =7.6 in the Pr state in contrast to a pKa >11 in the Pfr state, indicating a pH-dependent charge distribution and H-bond network in the Pr chromophore binding pocket around neutral pH. Here, we report on ultrafast UV/Vis absorption spectroscopy of the primary Pr photoisomerization of Agp2 at pH 6 and pH 9 and upon H2 O/D2 O buffer exchange. The triexponential Pr kinetics slows down at increased pH and pronounced pH-dependent kinetic isotope effects are observed. The results on the Pr photoreaction suggest: 1) component-wise hindered dynamics on the chromophore excited-state potential energy surface at high pH and 2) proton translocation processes either via single-proton transfer or via significant reorganization of H-bond networks. Both effects reflect the interplay between the pH-dependent charge distribution in the Pr chromophore binding pocket on the one hand and chromophore excitation and its Z→E isomerization on the other hand.
authors.affiliation: Department of Physics, University of Kaiserslautern, Erwin-Schrödinger-Strasse, Geb. 46, 67663, Kaiserslautern, Germany), Fax: +49-631-205-3902.
authors.forename: Patrick
authors.initials: P
authors.lastname: Singer
authors.affiliation: Botanical Institute, Karlsruhe Institute of Technology, Kaiserstraße 2, 76131, Karlsruhe, Germany.
authors.forename: Sybille
authors.initials: S
authors.lastname: Wörner
authors.affiliation: Botanical Institute, Karlsruhe Institute of Technology, Kaiserstraße 2, 76131, Karlsruhe, Germany.
authors.forename: Tilman
authors.initials: T
authors.lastname: Lamparter
authors.affiliation: Department of Physics, University of Kaiserslautern, Erwin-Schrödinger-Strasse, Geb. 46, 67663, Kaiserslautern, Germany), Fax: +49-631-205-3902. diller@physik.uni-kl.de.
authors.forename: Rolf
authors.identifier: 0000-0002-3629-8334
authors.initials: R
authors.lastname: Diller
mesh_terms: D060054:Agrobacterium / Q000737:chemistry*; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D055668:Photochemical Processes; D010834:Phytochrome / Q000737:chemistry*; D013057:Spectrum Analysis / Q000379:methods*
chemical_list: D010834:Phytochrome
keywords: bathy phytochrome; isomerization; kinetic isotope effect; photochemistry; ultrafast spectroscopy