title: Bacteriorhodopsin's M412 intermediate contains a 13-cis, 14-s-trans, 15-anti-retinal Schiff base chromophore.
abstract: The structure of the retinal chromophore about the C = N and C14-C15 bonds in bacteriorhodopsin's M412 intermediate has been determined by analyzing resonance Raman spectra of 2H and 13C isotopic derivatives. Normal mode calculations on 13-cis-retinal Schiff bases demonstrate that the C15-D rock and N-CLys stretch are strongly coupled for C = N-syn chromophores and weakly coupled for C = N-anti chromophores. When the Schiff base geometry is anti, the C15-D rock appears as a localized resonance Raman active mode at approximately 980 cm-1, which is moderately sensitive to 13C substitution at positions 14 and 15 (approximately 7 cm-1) and insensitive to 13C substitution at the epsilon position of lysine. When the Schiff base geometry is syn, in-phase and out-of-phase combinations of the C15-D rock and N-CLys stretch are predicted at approximately 1060 and approximately 910 cm-1, respectively. The in-phase mode is more sensitive to 13C substitution at positions 14 and 15 (approximately 15 cm-1) and at the epsilon position of lysine (approximately 4 cm-1). Calculations and comparison with experimental data on dark-adapted bacteriorhodopsin indicate that the in-phase mode at approximately 1060 cm-1 carries the majority of the resonance Raman intensity. M412 exhibits a C15-D rock at 968 cm-1 that shifts 8 cm-1 when 13C is added at positions 14 and 15 and is insensitive to 13C substitution at the epsilon-position of lysine. This demonstrates that M412 contains a C = N-anti Schiff base.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Chemistry, University of California, Berkeley 94720.
authors.forename: J B
authors.initials: JB
authors.lastname: Ames
authors.forename: S P
authors.initials: SP
authors.lastname: Fodor
authors.forename: R
authors.initials: R
authors.lastname: Gebhard
authors.forename: J
authors.initials: J
authors.lastname: Raap
authors.forename: E M
authors.initials: EM
authors.lastname: van den Berg
authors.forename: J
authors.initials: J
authors.lastname: Lugtenburg
authors.forename: R A
authors.initials: RA
authors.lastname: Mathies
mesh_terms: D001436:Bacteriorhodopsins / Q000378:metabolism*; D006217:Halobacterium / Q000378:metabolism; D007700:Kinetics; D012172:Retinaldehyde / Q000378:metabolism*; D012176:Retinoids / Q000378:metabolism*; D012545:Schiff Bases; D013059:Spectrum Analysis, Raman / Q000379:methods; D013997:Time Factors
chemical_list: D012176:Retinoids; D012545:Schiff Bases; D001436:Bacteriorhodopsins; D012172:Retinaldehyde