Time-resolved resonance Raman analysis of chromophore structural changes in the formation and decay of rhodopsin's BSI intermediate.

Time-resolved resonance Raman microchip flow experiments are performed to obtain the vibrational spectrum of the chromophore in rhodopsin's BSI intermediate and to probe structural changes in the bathorhodopsin-to-BSI and BSI-to-lumirhodopsin transitions. Kinetic Raman spectra from 250 ns to 3 μs identify the key vibrational features of BSI. BSI exhibits relatively intense HOOP modes at 886 and 945 cm-1 that are assigned to C14H and C11HC12H Au wags, respectively. This result suggests that in the bathorhodopsin-to-BSI transition the highly strained all-trans chromophore has relaxed in the C10−C11C12−C13 region, but is still distorted near C14. The low frequency of the 11,12 Au HOOP mode in BSI compared with that of lumirhodopsin and metarhodopsin I indicates weaker coupling between the 11H and 12H wags due to residual distortion of the BSI chromophore near C11C12. The CNH+ stretching mode in BSI at 1653 cm-1 exhibits a normal deuteriation induced downshift of 23 cm-1, implying that there is no significant...