title: Direct measurement of the photoelectric response time of bacteriorhodopsin via electro-optic sampling.
abstract: The photovoltaic signal associated with the primary photochemical event in an oriented bacteriorhodopsin film is measured by directly probing the electric field in the bacteriorhodopsin film using an ultrafast electro-optic sampling technique. The inherent response time is limited only by the laser pulse width of 500 fs, and permits a measurement of the photovoltage with a bandwidth of better than 350 GHz. All previous published studies have been carried out with bandwidths of 50 GHz or lower. We observe a charge buildup with an exponential formation time of 1.68 +/- 0.05 ps and an initial decay time of 31.7 ps. Deconvolution with a 500-fs Gaussian excitation pulse reduces the exponential formation time to 1.61 +/- 0.04 ps. The photovoltaic signal continues to rise for 4.5 ps after excitation, and the voltage profile corresponds well with the population dynamics of the K state. The origin of the fast photovoltage is assigned to the partial isomerization of the chromophore and the coupled motion of the Arg-82 residue during the primary event.
authors.affiliation: Solid State Electronics Laboratory, Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, USA.
authors.forename: J
authors.initials: J
authors.lastname: Xu
authors.forename: A B
authors.initials: AB
authors.lastname: Stickrath
authors.forename: P
authors.initials: P
authors.lastname: Bhattacharya
authors.forename: J
authors.initials: J
authors.lastname: Nees
authors.forename: G
authors.initials: G
authors.lastname: Váró
authors.forename: J R
authors.initials: JR
authors.lastname: Hillebrecht
authors.forename: L
authors.initials: L
authors.lastname: Ren
authors.forename: R R
authors.initials: RR
authors.lastname: Birge
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry / Q000502:physiology* / Q000528:radiation effects*; D004563:Electrochemistry / Q000295:instrumentation / Q000379:methods*; D008027:Light; D008564:Membrane Potentials / Q000502:physiology* / Q000528:radiation effects*; D055095:Optics and Photonics / Q000295:instrumentation; D010775:Photic Stimulation / Q000379:methods; D010777:Photochemistry / Q000295:instrumentation / Q000379:methods*; D011930:Reaction Time / Q000502:physiology*; D055672:Static Electricity
chemical_list: D001436:Bacteriorhodopsins