ULTRAFAST SPECTROSCOPY OF RHODOPSINS - PHOTOCHEMISTRY AT ITS BEST

Recent advances in laser technology now allow us to study the ultrafas t primary photochemical events in rhodopsin, bacteriorhodopsin, and ha lorhodopsin in real time. The results of various ultrafast studies of rhodopsins are reviewed with an emphasis on (1) the relationship betwe en the reaction rate and reaction efficiency and its implications for the mechanism of isomerization, (2) the homogeneity of the reaction pa thways, and (3) the role of the protein in the reaction dynamics. The results mandate the introduction of a new paradigm to describe these u ltrafast reactions that specifically considers the importance of the t imescale of vibrational dephasing and relaxation relative to the react ive motion and the contribution of vibrational coherence to the reacti on mechanism.