Nanosecond time-resolved infrared spectroscopy distinguishes two K species in the bacteriorhodopsin photocycle.
The photochemical reaction process of bacteriorhodopsin in the nanosecond time range (-120-860 ns) was measured in the 1400-900 cm-1 region with an improved time resolved dispersive-type infrared spectrometer. The system is equipped with a newly developed detection unit whose instrumental response to a 5-ns laser pulse has a full width of the half-maximum of 60 ns. It provides highly accurate data that enabled us to extract a kinetic process one order of magnitude faster than the instrumental response. The spectral changes in the 1400-900 cm-1 region were analyzed by singular value decomposition and resolved into three components. These components were separated by fitting with 10- and 1000-ns exponential functions and a step function, which were convoluted with the instrumental response function. The components with decay time constants of 10 and 1000 ns are named K and KL, respectively, on the basis of previous visible spectroscopy. The spectral shapes of K and KL are distinguishable by their hydrogen-out-of-plane (HOOP) modes, at 958 and 984 cm-1, respectively. The former corresponds to the K intermediate recorded at 77 K and the latter to a K-like photoproduct at 135 K. On the basis of published data, these bands are assigned to the 15-HOOP mode, indicating that the K and KL differ in a twist around the C14-C15 bond.
Sasaki
J
J
Department of Biophysics, Faculty of Science, Kyoto University, Japan.
Yuzawa
T
T
Kandori
H
H
Maeda
A
A
Hamaguchi
H
H
D001436:Bacteriorhodopsins / Q000378:metabolism* / Q000528:radiation effects; D006217:Halobacterium / Q000378:metabolism*; D007700:Kinetics; D008027:Light; D008433:Mathematics; D008962:Models, Theoretical; D013055:Spectrophotometry, Infrared; D013997:Time Factors
D001436:Bacteriorhodopsins