Ultrafast isomerization dynamics of retinal in bacteriorhodopsin as revealed by femtosecond absorption spectroscopy

摘要

A femtosecond (fs) broad-band absorption apparatus was used to measure the early photoisomerization process of bacteriorhodopsin's (BR) photocycle to reveal the character of the important intermediate of J(625) and to obtain a deeper understanding of the role of photoisomerization in BR photocycle. Two time constants of 0.5 ps (95%) and 2.0 ps (5%) were brought out by global fitting on thirty curves in the near-infrared region. We suggest that the first time constant results from the decay of I-460 intermediate, and the longer component might be associated with BR isomer. The global analysis over 450, 540, 630, 710 and 870 nm traces identified two time constants, similar to 0.5 and similar to 3 ps. The slower component can be extracted from the processes of both J(625) -> BR568 (540 nm) and J(625) -> K-590 (630 nm), suggesting J-intermediate takes a partial cis configuration. The obvious negative feature in early delay time of 700-780 nm regions was attributed to the radiative transition (stimulated emission) from the Franck-Condon active configuration along the isomerization potential surface of all-trans-retinal.