VIBRATIONAL-RELAXATION DURING THE RETINAL ISOMERIZATION IN BACTERIORHODOPSIN

Femtosecond time-resolved optical pump-infrared probe spectroscopy was employed to characterize the ethylenic (C=C)-stretch vibrational dyna mics (1498-1542 cm(-1)) of the retinal chromophore in Bacteriorhodopsi n (BR) during the initial, all-trans to 13-cis isomerization. The earl y branching reaction was observed, i.e. formation of the ground-state 13-cis product, K, and partial recovery of the all-trans educt state B R570. The BR570 recovery occurs within 2 ps and thus is faster than K- formation (3-4 ps). The IR transients are described in terms of a kine tic model involving vibrational precursors for K and for the recoverin g BR570, respectively. (C) 1998 Elsevier Science B.V. All rights reser ved.