title: Chromophore motion during the bacteriorhodopsin photocycle: polarized absorption spectroscopy of bacteriorhodopsin and its M-state in bacteriorhodopsin crystals.
abstract: The three-dimensional crystallization of bacteriorhodopsin was systematically investigated and the needle-shaped crystal form analysed. In these crystals the M-intermediate forms 10 times faster and decays 15 times more slowly than in purple membranes. Polarized absorption spectra of the crystals were measured in the dark and light adapted states. A slight decrease in the angle between the transition moment and the membrane plane was detected during dark adaptation. The crystallization of a mutated bacteriorhodopsin, in which the aspartic acid at residue 96 was replaced by asparagine, provided crystals with a long lived M-intermediate. This allowed polarized absorption measurements of the M-chromophore. The change in the polarization ratio upon formation of the M-intermediate indicates an increase in the angle between the main transition dipole and the membrane plane by 2.2 degrees +/- 0.5, corresponding to a 0.5 A displacement of one end of the chromophore out of the membrane plane of the bacteriorhodopsin molecule.
authors.affiliation: Max-Planck-Institut für Biochemie, Martinsried, FRG.
authors.forename: G F
authors.initials: GF
authors.lastname: Schertler
authors.forename: R
authors.initials: R
authors.lastname: Lozier
authors.forename: H
authors.initials: H
authors.lastname: Michel
authors.forename: D
authors.initials: D
authors.lastname: Oesterhelt
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000235:genetics; D003460:Crystallization; D006217:Halobacterium / Q000378:metabolism; D007700:Kinetics; D015591:Microspectrophotometry; D009154:Mutation; D010777:Photochemistry; D011487:Protein Conformation
chemical_list: D001436:Bacteriorhodopsins