Article Information

• PDF (691 kb)

PubMed

• Articles by G.I. Groma
• Articles by J. Kuhl

Related Articles

• Vibrational Spectrum of the Lumi Intermediate in the Room Te...

  Vibrational Spectrum of the Lumi Intermediate in the Room Temperature Rhodopsin Photo-Reaction Biophysical Journal, Volume 74, Issue 3, 1 March 1998, Pages 1492-1501 Laszlo Ujj, Frank Jäger and George H. Atkinson Abstract The vibrational spectrum (650–1750cm) of the lumi-rhodopsin (lumi) intermediate formed in the microsecond time regime of the room-temperature rhodopsin (Rh) photoreaction is measured for the first time using picosecond time-resolved coherent anti-Stokes Raman spectroscopy (PTR/CARS). The vibrational spectrum of lumi is recorded 2.5s after the 3-ps, 500-nm excitation of Rh. Complementary to Fourier transform infrared spectra recorded at Rh sample temperatures low enough to freeze lumi, these PTR/CARS results provide the first detailed view of the vibrational degrees of freedom of room-temperature lumi (lumi) through the identification of 21 bands. The exceptionally low intensity (compared to those observed in batho) of the hydrogen out-of-plane (HOOP) bands, the moderate intensity and absolute positions of C-C stretching bands, and the presence of high-intensity CC stretching bands suggest that lumi contains an almost planar (nontwisting), all- retinal geometry. Independently, the 944-cm position of the most intense HOOP band implies that a resonance coupling exists between the out-of-plane retinal vibrations and at least one group among the amino acids comprising the retinal binding pocket. The formation of lumi, monitored via PTR/CARS spectra recorded on the nanosecond time scale, can be associated with the decay of the blue-shifted intermediate (BSI) formed in equilibrium with the batho intermediate. PTR/CARS spectra measured at a 210-ns delay contain distinct vibrational features attributable to BSI, which suggest that the all- retinal in both BSI and lumi is strongly coupled to part of the retinal binding pocket. With regard to the energy storage/transduction mechanism in Rh, these results support the hypothesis that during the formation of lumi, the majority of the photon energy absorbed by Rh transfers to the apoprotein opsin. Abstract | Full Text | PDF (259 kb)

• Ultrafast Dynamics of Phytochrome from the Cyanobacterium Sy...

  Ultrafast Dynamics of Phytochrome from the Cyanobacterium Synechocystis, Reconstituted with Phycocyanobilin and Phycoerythrobilin Biophysical Journal, Volume 82, Issue 2, 1 February 2002, Pages 1004-1016 Karsten Heyne, Johannes Herbst, Dietmar Stehlik, Berta Esteban, Tilman Lamparter, Jon Hughes and Rolf Diller Abstract Femtosecond time-resolved transient absorption spectroscopy was employed to characterize for the first time the primary photoisomerization dynamics of a bacterial phytochrome system in the two thermally stable states of the photocycle. The 85-kDa phytochrome Cph1 from the cyanobacterium PCC 6803 expressed in was reconstituted with phycocyanobilin (Cph1-PCB) and phycoerythrobilin (Cph1-PEB). The red-light-absorbing form Pr of Cph1-PCB shows an ∼150 fs relaxation in the S state after photoexcitation at 650nm. The subsequent Z-E isomerization between rings C and D of the linear tetrapyrrole-chromophore is best described by a distribution of rate constants with the first moment at (16ps). Excitation at 615nm leads to a slightly broadened distribution. The reverse E-Z isomerization, starting from the far-red-absorbing form Pfr, is characterized by two shorter time constants of 0.54 and 3.2ps. In the case of Cph1-PEB, double-bond isomerization does not take place, and the excited-state lifetime extends into the nanosecond regime. Besides a stimulated emission rise time between 40 and 150 fs, no fast relaxation processes are observed. This suggests that the chromophore-protein interaction along rings A, B, and C does not contribute much to the picosecond dynamics observed in Cph1-PCB but rather the region around ring D near the isomerizing CC double bond. The primary reaction dynamics of Cph1-PCB at ambient temperature is found to exhibit very similar features as those described for plant type A phytochrome, i.e., a relatively slow Pr, and a fast Pfr, photoreaction. This suggests that the initial reactions were established already before evolution of plant phytochromes began. Abstract | Full Text | PDF (400 kb)

• Direct Measurement of the Photoelectric Response Time of Bac...

  Direct Measurement of the Photoelectric Response Time of Bacteriorhodopsin via Electro-Optic Sampling Biophysical Journal, Volume 85, Issue 2, 1 August 2003, Pages 1128-1134 J. Xu, A.B. Stickrath, P. Bhattacharya, J. Nees, G. Váró, J.R. Hillebrecht, L. Ren and R.R. Birge 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 350GHz. All previous published studies have been carried out with bandwidths of 50GHz or lower. We observe a charge buildup with an exponential formation time of 1.68±0.05ps and an initial decay time of 31.7ps. Deconvolution with a 500-fs Gaussian excitation pulse reduces the exponential formation time to 1.61±0.04ps. The photovoltaic signal continues to rise for 4.5ps 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. Abstract | Full Text | PDF (440 kb)

• …more

Abstract

Dried oriented purple membrane samples of Halobacterium salinarium were excited by 150 fs laser pulses of 620 nm with a 7 kHz repetition rate. An unusual complex picosecond electric response signal consisting of a positive and a negative peak was detected by a sampling oscilloscope. The ratio of the two peaks was changed by 1) reducing the repetition rate, 2) varying the intensity of the excitation beam, and 3) applying background illumination by light of 647 nm or 511 nm. All of these features can be explained by the simultaneous excitation of the bacteriorhodopsin ground form and the K intermediate. The latter was populated by the (quasi)continuous excitation attributable to its prolonged lifetime in a dehydrated state. Least-square analysis resulted in a 5 ps upper and 2.5 ps lower limit for the time constant of the charge displacement process, corresponding to the forward reaction. That is in good agreement with the formation time of K. The charge separation driven by the reverse phototransition was faster, having a time constant of a 3.5 ps upper limit. The difference in the rates indicates the existence of different routes for the forward and the reverse photoreactions.