Direct observation of the femtosecond excited-state cis-trans isomerization in bacteriorhodopsin.
Femtosecond optical measurement techniques have been used to study the primary photoprocesses in the light-driven transmembrane proton pump bacteriorhodopsin. Light-adapted bacteriorhodopsin was excited with a 60-femtosecond pump pulse at 618 nanometers, and the transient absorption spectra from 560 to 710 nanometers were recorded from -50 to 1000 femtoseconds by means of 6-femtosecond probe pulses. By 60 femtoseconds, a broad transient hole appeared in the absorption spectrum whose amplitude remained constant for about 200 femtoseconds. Stimulated emission in the 660- to 710-nanometer region and excited-state absorption in the 560- to 580-nanometer region appeared promptly and then shifted and decayed from 0 to approximately 150 femtoseconds. These spectral features provide a direct observation of the 13-trans to 13-cis torsional isomerization of the retinal chromophore on the excited-state potential surface. Absorption due to the primary ground-state photoproduct J appears with a time constant of approximately 500 femtoseconds.
Mathies
R A
RA
Department of Chemistry, University of California, Berkeley 94720.
Brito Cruz
C H
CH
Pollard
W T
WT
Shank
C V
CV
D001436:Bacteriorhodopsins; D006217:Halobacterium / Q000032:analysis; D007536:Isomerism; D010777:Photochemistry; D013053:Spectrophotometry; D013237:Stereoisomerism
D001436:Bacteriorhodopsins