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MO: Molekülphysik
MO 45: Biomolecules II
MO 45.6: Talk
Wednesday, March 15, 2006, 17:45–18:00, H10
First Steps of Retinal Photoisomerization in Proteorhodopsin — •Martin O. Lenz1, Robert Huber1, Bernhard Schmidt2, Peter Gilch2, Rolf Kalmbach3, Martin Engelhard3, and Josef Wachtveitl1 — 1Institut für Physikalische und Theoretische Chemie, Marie-Curie-Str. 11, Johann-Wolfgang-Goethe-Universität Frankfurt, 60439 Frankfurt am Main — 2Universität München, Department für Physik, Lehrstuhl für BioMolekulare Optik, Oettingenstraße 67, 80538 München — 3Max-Planck-Institute of Molecular Physiology, Department of Physical Biochemistry, Otto-Hahn-Str. 11, 44227 Dortmund
The early steps (< 1 ns) in the photocycle of the proton pump proteorhodopsin (PR) are analyzed by ultrafast spectroscopic techniques. A comparison to the first primary events of well known retinal proteins like the archaeal proton pump bacteriorhodopsin (BR) is given. A dynamic Stokes shift observed in fs-time resolved fluorescence experiments allows a direct observation of early motions on the excited state potential energy surface. The initial dynamics is dominated by sequentially emerging stretching (<150 fs) and torsional (~300 fs) modes of the retinal. The different protonation states of the primary proton acceptor Asp97 drastically affect the reaction rate and the overall quantum efficiencies of the isomerization reactions mainly evidenced for time scales above 1 ps. However, no major influence on the fast time scales could be seen, indicating that the movement out of the Franck-Condon region is fairly robust to electrostatic changes in the retinal binding pocket. Taking into account investigations on the primary events of BR a reaction scheme is presented.