Water structural changes in the bacteriorhodopsin photocycle: analysis by Fourier transform infrared spectroscopy.
The Fourier transform infrared difference spectra between light-adapted bacteriorhodopsin (BR) and its photointermediates, L and M, were analyzed for the 3750-3450-cm-1 region. The O-H stretching vibrational bands were identified from spectra upon substitution with 2H2O. Among them, the 3642-cm-1 band of BR was assigned to water by substitution with H2(18)O. By a comparison with the published infrared spectra of the water in model systems [Mohr, S.C., Wilk, W.D., & Barrow, G.M. (1965) J. Am. Chem. Soc. 87, 3048-3052], it is shown that the O-H bonds of the water in BR interact very weakly. Upon formation of L, the interaction becomes stronger. The O-H bonds of the protein side chain undergo similar changes. On the other hand, M formation further weakens the interaction of the same water molecules in BR. The appearance of a sharp band at 3486 cm-1, which was assigned tentatively to the N-H stretching vibration of the peptide bond, is unique to L. The results suggest that the water molecules are involved in the perturbation of Asp-96 in the L intermediate and that they are exerted from the protonated Schiff base which changes position upon the light-induced reaction.
Maeda
A
A
Department of Biophysics, Faculty of Science, Kyoto University, Japan.
Sasaki
J
J
Shichida
Y
Y
Yoshizawa
T
T
D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000302:isolation & purification; D003903:Deuterium / Q000737:chemistry; D005583:Fourier Analysis; D006217:Halobacterium / Q000737:chemistry; D006860:Hydrogen Bonding; D008958:Models, Molecular; D010103:Oxygen Isotopes; D012545:Schiff Bases; D013055:Spectrophotometry, Infrared; D014867:Water / Q000737:chemistry*
D010103:Oxygen Isotopes; D012545:Schiff Bases; D014867:Water; D001436:Bacteriorhodopsins; D003903:Deuterium