title: The first step in vision occurs in femtoseconds: complete blue and red spectral studies.
abstract: Femtosecond transient absorption measurements of the cis-trans isomerization of the visual pigment rhodopsin clarify the interpretation of the dynamics of the first step in vision. We present femtosecond time-resolved spectra as well as kinetic measurements at specific wavelengths between 490 and 670 nm using 10-fs probe pulses centered at 500 and 620 nm following a 35-fs pump pulse at 500 nm. The expanded spectral window beyond that available (500-570 nm) in our previous study [Schoenlein, R. W., Peteanu, L. A., Mathies, R. A. & Shank, C. V. (1991) Science 254, 412-415] provides the full differential absorption spectrum of the photoproduct as a function of delay time after photolysis. The high time-resolution data presented here contradict an alternative interpretation of the rhodopsin photochemistry offered by Callender and co-workers [Yan, M., Manor, D., Weng, G., Chao, H., Rothberg, L., Jedju, T. M., Alfano, R. R. & Callender, R. H. (1991) Proc. Natl. Acad. Sci. USA 88, 9809-9812]. Our results confirm that the red-shifted (lambda max approximately 570 nm) photo-product of the isomerization reaction is fully formed within 200 fs. Subsequent changes in the differential spectra between 200 fs and 6 ps are attributed to a combination of dynamic ground-state processes such as intramolecular vibrational energy redistribution, vibrational cooling, and conformational relaxation.
authors.affiliation: Department of Chemistry, University of California, Berkeley 94720.
authors.forename: L A
authors.initials: LA
authors.lastname: Peteanu
authors.forename: R W
authors.initials: RW
authors.lastname: Schoenlein
authors.forename: Q
authors.initials: Q
authors.lastname: Wang
authors.forename: R A
authors.initials: RA
authors.lastname: Mathies
authors.forename: C V
authors.initials: CV
authors.lastname: Shank
mesh_terms: D003118:Color Perception / Q000502:physiology*; D006801:Humans; D007700:Kinetics; D012243:Rhodopsin / Q000737:chemistry / Q000378:metabolism; D013053:Spectrophotometry; D013997:Time Factors; D014785:Vision, Ocular / Q000502:physiology*
chemical_list: D012243:Rhodopsin