Solid-state sup 13 C and sup 15 N NMR study of the low pH forms of bacteriorhodopsin

Journal Article · Tue Jul 24 04:00:00 EDT 1990 · Biochemistry; (USA)

DOI:https://doi.org/10.1021/bi00481a017· OSTI ID:6400926

de Groot, H J; Smith, S O; Courtin, J; van den Berg, E; Winkel, C; Lugtenburg, J; Griffin, R G; Herzfeld, J ^[1]

---

1. Massachusetts Institute of Technology, Cambridge (USA)

The visible absorption of bacteriorhodopsin (bR) is highly sensitive to pH, the maximum shifting from 568 nm (pH 7) to approximately 600 nm (pH 2) and back to 565 nm (pH 0) as the pH is decreased further with HCl. Blue membrane is also formed by deionization of neutral purple membrane suspensions. Low-temperature, magic angle spinning 13C and 15N NMR was used to investigate the transitions to the blue and acid purple states. The 15N NMR studies involved (epsilon-15N)lysine bR, allowing a detailed investigation of effects at the Schiff base nitrogen. The 15N resonance shifts approximately 16 ppm upfield in the neutral purple to blue transition and returns to its original value in the blue to acid purple transition. Thus, the 15N shift correlates directly with the color changes, suggesting an important contribution of the Schiff base counterion to the opsin shift. The results indicate weaker hydrogen bonding in the blue form than in the two purple forms and permit a determination of the contribution of the weak hydrogen bonding to the opsin shift at a neutral pH of approximately 2000 cm-1. An explanation of the mechanism of the purple to blue to purple transition is given in terms of the complex counterion model. The 13C NMR experiments were performed on samples specifically 13C labeled at the C-5, C-12, C-13, C-14, or C-15 positions in the retinylidene chromophore. The effects of the purple to blue to purple transitions on the isotropic chemical shifts for the various 13C resonances are relatively small. It appears that bR600 consists of at least four different species. The data confirm the presence of 13-cis- and all-trans-retinal in the blue form, as in neutral purple dark-adapted bR. All spectra of the blue and acid purple bR show substantial inhomogeneous broadening which indicates additional irregular distortions of the protein lattice.

• OSTI ID: 6400926
• Journal Information: Biochemistry; (USA), Journal Name: Biochemistry; (USA) Vol. 29:29; ISSN 0006-2960; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
140505* -- Solar Energy Conversion-- Photochemical
Photobiological
& Thermochemical Conversion-- (1980-)
550201 -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
AMINO ACIDS
CARBON 13
CARBON ISOTOPES
CARBOXYLIC ACIDS
CHEMICAL SHIFT
CONFORMATIONAL CHANGES
EVEN-ODD NUCLEI
IMINES
ISOTOPE APPLICATIONS
ISOTOPES
LIGHT NUCLEI
LYSINE
MAGNETIC RESONANCE
MEMBRANES
MOLECULAR STRUCTURE
NITROGEN 15
NITROGEN ISOTOPES
NMR SPECTRA
NUCLEAR MAGNETIC RESONANCE
NUCLEI
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PH VALUE
PHOTOSYNTHETIC MEMBRANES
PIGMENTS
PROTEINS
RESONANCE
RHODOPSIN
SCHIFF BASES
SPECTRA
STABLE ISOTOPES
TRACER TECHNIQUES