title: Fourier transform infrared difference spectroscopy of bacteriorhodopsin and its photoproducts.
abstract: Fourier transform infrared difference spectroscopy has been used to obtain the vibrational modes in the chromophore and apoprotein that change in intensity or position between light-adapted bacteriorhodopsin and the K and M intermediates in its photocycle and between dark-adapted and light-adapted bacteriorhodopsin. Our infrared measurements provide independent verification of resonance Raman results that in light-adapted bacteriorhodopsin the protein-chromophore linkage is a protonated Schiff base and in the M state the Schiff base is unprotonated. Although we cannot unambiguously identify the Schiff base stretching frequency in the K state, the most likely interpretation of deuterium shifts of the chromophore hydrogen out-of-plane vibrations is that the Schiff base in K is protonated. The intensity of the hydrogen out-of-plane vibrations in the K state compared with the intensities of those in light-adapted and dark-adapted bacteriorhodopsin shows that the conformation of the chromophore in K is considerably distorted. In addition, we find evidence that the conformation of the protein changes during the photocycle.
mesh_terms: D001436:Bacteriorhodopsins / Q000528:radiation effects; D002338:Carotenoids / Q000528:radiation effects; D005583:Fourier Analysis; D009038:Motion; D010777:Photochemistry; D011487:Protein Conformation; D013055:Spectrophotometry, Infrared
chemical_list: D002338:Carotenoids; D001436:Bacteriorhodopsins