C14-C15 single bond isomerizations of the retinal chromophore involved in the proton-pumping mechanism of bacteriorhodopsin
Resonance Raman spectroscopy is used to examine the possibility that C14-C15 single bond isomerizations of the retinal prosthetic group are involved in the photochemical reactions of bacteriorhodopsin. Normal mode calculations show that the vibration that contains predominantly C14-C15 stretch character is approximately equal to 70 cm-1 lower in frequency in the 14-s-cis conformer than in the s-trans case. This geometric effect is insensitive to out-of-plane twists and should be observed in the sterically hindered 13-cis, 14-s-cis retinal protonated Schiff base, which has been proposed as the chromophore in the K and L intermediates of bacteriorhodopsin. Resonance Raman spectra were obtained of K625 by using the low temperature (77 K) spinning-cell technique. Isotopic substitutions with 13C and 2H show that significant C14-C15 stretch character is observed in normal modes at approximately equal to 1185-1195 cm-1. The relatively high frequency of the C14-C15 stretch argues that K625 contains a 13-cis, 14-s-trans chromophore. Similarly, isotopic derivatives show that L550 has a localized C14-C15 stretch at 1172 cm-1, consistent with a 14-s-trans chromophore. These results argue that the primary step in bacteriorhodopsin is a C13=C14 trans----cis photoisomerization that does not involve C14-C15 s-cis structures.
- Research Organization:
- Univ. of California, Berkeley
- OSTI ID:
- 5630052
- Journal Information:
- Proc. Natl. Acad. Sci. U.S.A.; (United States), Journal Name: Proc. Natl. Acad. Sci. U.S.A.; (United States) Vol. 4; ISSN PNASA
- Country of Publication:
- United States
- Language:
- English
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
BARYONS
CARBON 13
CARBON ISOTOPES
CAROTENOIDS
CHEMICAL REACTIONS
DEUTERIUM
ELEMENTARY PARTICLES
EVEN-ODD NUCLEI
FERMIONS
HADRONS
HYDROCARBONS
HYDROGEN ISOTOPES
IMINES
ISOMERIZATION
ISOTOPES
LASER SPECTROSCOPY
LIGHT NUCLEI
NUCLEI
NUCLEONS
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOSYNTHETIC BACTERIA
PIGMENTS
PROTEINS
PROTONS
RAMAN SPECTRA
RAMAN SPECTROSCOPY
RHODOPSIN
SCHIFF BASES
SPECTRA
SPECTROSCOPY
STABLE ISOTOPES
TERPENES