Nuclear magnetic resonance study of the Schiff base in bacteriorhodopsin: Counterion effects on the sup 15 N shift anisotropy

Journal Article · Tue Apr 18 04:00:00 EDT 1989 · Biochemistry; (USA)

DOI:https://doi.org/10.1021/bi00434a033· OSTI ID:5546114

de Groot, H J.M.; Harbison, G S; Herzfeld, J; Griffin, R G ^[1]

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1. Massachusetts Institute of Technology, Cambridge (USA)

High-resolution, solid-state {sup 15}N NMR has been used to study the chemical shift anisotropies of the Schiff bases in bacteriorhodopsin (bR) and in an extensive series of model compounds. Using slow-spinning techniques, the authors are able to obtain sufficient rotational sideband intensity to determine the full {sup 15}N chemical shift anisotropy for the Schiff base nitrogen in bR{sub 548} and bR{sub 568}. Comparisons are made between all-trans-bR{sub 568} and N-all-trans-retinylidene butylimine salts with halide, phenolate, and carboxylate counterions. It is argues that for the model compounds the variation in {sup 15}N chemical shift reflects the variation in (hydrogen) bond strength with the various counterions. The results suggest that carboxylates and tyrosinates may form hydrogen bonds of comparable strength in a hydrophobic environment. Thus, the hydrogen bonding strength of a counterion depends on factors that are not completely reflected in the solution pK{sub a} of its conujugate acid. For the model compounds, the two most downfield principal values of the {sup 15}N chemical shift tensor, {sigma}{sub 22} and {sigma}{sub 33}, vary dramatically with different counterions, whereas {sigma}{sub 11} remains essentially unaffected. In addition, there exists a linear correlation between {sigma}{sub 22} and {sigma}{sub 33}, which suggests that a single mechanism is responsible for the variation in chemical shifts present in all three classes of model compounds. The data for bR{sub 568} follow this trend, but the isotropic shift is 11 ppm further upfield than any of the model compounds. This extreme value suggests an unusually weak hydrogen bond in the protein.

• OSTI ID: 5546114
• Journal Information: Biochemistry; (USA), Journal Name: Biochemistry; (USA) Vol. 28:8; ISSN 0006-2960; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

550601* -- Medicine-- Unsealed Radionuclides in Diagnostics
62 RADIOLOGY AND NUCLEAR MEDICINE
AMINO ACIDS
ANISOTROPY
AROMATICS
CARBOXYLIC ACIDS
CHEMICAL BONDS
CHEMICAL SHIFT
HYDROXY ACIDS
HYDROXY COMPOUNDS
IMINES
ISOTOPES
LIGHT NUCLEI
LYSINE
MAGNETIC RESONANCE
MATHEMATICAL MODELS
MOLECULAR MODELS
NITROGEN 15
NITROGEN ISOTOPES
NUCLEAR MAGNETIC RESONANCE
NUCLEI
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHENOLS
PIGMENTS
PROTEINS
RESONANCE
RHODOPSIN
SCHIFF BASES
STABLE ISOTOPES
TYROSINE