Determination of retinal Schiff base configuration in bacteriorhodopsin
Resonance Raman spectra of the BR/sub 568/, BR/sub 548/, K/sub 625/, and L/sub 550/ intermediates of the bacteriorhodopsin photocycle have been obtained in /sup 1/H/sub 2/O and /sup 2/H/sub 2/O by using native purple membrane as well as purple membrane regenerated with 14,15-/sup 13/C/sub 2/ and 12,14-/sup 2/H/sub 2/ isotopic derivatives of retinal. These derivatives were selected to determine the contribution of the C/sub 14/-C/sub 15/ stretch to the normal modes in the 1100- to 1400-cm/sup -1/ fingerprint region and to characterize the coupling of the C/sub 14/-C/sub 15/ stretch with the NH rock. Normal mode calculations demonstrate that when the retinal Schiff base is in the C=N cis configuration the C/sub 14/-C/sub 15/ stretch and the NH rock are strongly coupled, resulting in a large (approx. =50-cm/sup -1/) upshift of the C/sub 14/-C/sub 15/ stretch upon deuteration of the Schiff base nitrogen. In the C=N trans geometry these vibrations are weakly coupled and only a slight (<5-cm/sup -1/) upshift of the C/sub 14/-C/sub 15/ stretch is predicted upon N-deuteration. In BR/sub 568/, the insensitivity of the 1201-cm/sup -1/ C/sub 14/-C/sub 15/ stretch to N-deuteration demonstrates that its retinal C=N configuration is trans. The C/sub 14/-C/sub 15/ stretch in BR/sub 548/, however, shifts up from 1167 cm/sup -1/ in /sup 1/H/sub 2/O to 1208 cm/sup -1/ in /sup 2/H/sub 2/O, indicating that BR/sub 548/ contains a C=N cis chromophore. Thus, the conversion of BR/sub 568/ to BR/sub 548/ (dark adaptation) involves isomerization about the C=N bond in addition to isomerization about the C/sub 13/=C/sub 14/ bond.
- Research Organization:
- Univ. of California, Berkeley
- OSTI ID:
- 6029141
- Journal Information:
- Proc. Natl. Acad. Sci. U.S.A.; (United States), Journal Name: Proc. Natl. Acad. Sci. U.S.A.; (United States) Vol. 81:7; ISSN PNASA
- Country of Publication:
- United States
- Language:
- English
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59 BASIC BIOLOGICAL SCIENCES
BIOLOGICAL ADAPTATION
CARBON 13
CARBON ISOTOPES
CELL CONSTITUENTS
CELL MEMBRANES
CHEMICAL REACTIONS
CHEMICAL SHIFT
ELECTROMAGNETIC RADIATION
EVEN-ODD NUCLEI
IMINES
ISOMERIZATION
ISOTOPE APPLICATIONS
ISOTOPES
LABELLED COMPOUNDS
LIGHT NUCLEI
MEMBRANES
MOLECULAR STRUCTURE
NUCLEI
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PIGMENTS
PROTEINS
RADIATIONS
RAMAN SPECTRA
RHODOPSIN
SCHIFF BASES
SPECTRA
STABLE ISOTOPES
TRACER TECHNIQUES
VISIBLE RADIATION