SCIENCE 2002, 297(5582), 822-825

The vibrational dynamics of the retinal chromophore all-trans-to-13-cis photoisomerization in bacteriorhodopsin has been studied with mid-infrared absorption spectroscopy at high time resolution (about 200 femtoseconds). After photoexcitation of light-adapted bacteriorhodopsin, the transient infrared absorption was probed in a broad spectral region, including vibrations with dominant C-C, C=C and C=NH stretching mode amplitude. All photoproduct modes, especially those around 1190 cm^-1 that are indicative for a 13-cis configuration of the chromophore, rise with a time constant of ~0.5 picosecond. The results presented give direct vibrational-spectroscopic evidence for the isomerization taking place within 0.5 picosecond, as has been suggested by previous optical femtosecond time-resolved experiments but questioned recently by picosecond time-resolved vibrational spectroscopy experiments.

DOI 10.1126/science.1072144