PROTON NMR-STUDY OF THE CONFORMATION OF BRADYKININ - PH TITRATION

pH titration by 1H-NMR spectroscopy of the peptide hormone bradykinin was carried out in 2H2O. Assignment of all α-proton signals and of most of the other resonances permitted the extraction of vicinal coupling constants 3Jαβ,β′ from which side chain conformation of all residues could be followed and analyzed as a function of pH. It is shown that the ionization of the terminal COOH group affects simultaneously the Arg-9 and Phe-8 chemical shifts and side chain orientation, and the non-equivalence of the Gly-4 methylene protons. Cooperative effects along the peptide backbone or a folded structure of the C-terminal part of bradykinin could explain this effect. © 1979.