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Conformational analysis of thyrotropin releasing factor by proton magnetic resonance spectroscopy
Author(s) -
Montagut Martine,
Lemanceau Bernard,
Bellocq AnneMarie
Publication year - 1974
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1974.360131216
Subject(s) - chemistry , tautomer , imidazole , intramolecular force , deuterium , histidine , dihedral angle , chemical shift , crystallography , hydrogen bond , resonance (particle physics) , equilibrium constant , proton , nuclear magnetic resonance spectroscopy , stereochemistry , molecule , organic chemistry , physics , particle physics , quantum mechanics , enzyme
The proton magnetic resonance spectrum of thyrotropin releasing factor (TRF) in solution in deuterium oxide and deuterated dimethylsulfoxide (DMSO–d 6 ) has been analyzed. Two forms differing in cis – trans isomerism about the His‐Pro peptide bond are observed. From the temperature dependence of chemical shift of the amide protons, it is concluded that TRF in DMSO–d 6 does not contain intramolecular hydrogen bonds. Measurement of NHC α H coupling constant provides an estimate of the histidine dihedral angle ϕ. Structural information about the histidine side‐chain is deduced from C α HC β H coupling constants and from the nonequivalence of the two prolyl δ‐protons. In DMSO–d 6 , there is evidence for a tautomeric equilibrium corresponding to an exchange of imidazole proton between the two nitrogen atoms N‐δ and N‐ε. In water, the N‐εH tautomer is found to be the predominant tautomeric form of the imidazole ring. These results in combination with energy calculation, vibrational analysis, and carbon nmr studies allow the determination of the conformationof TRF.