STRUCTURAL DETERMINATION OF THE VASOACTIVE-INTESTINAL-PEPTIDE BY 2-DIMENSIONAL H-1-NMR SPECTROSCOPY

The structure of the vasoactive intestinal peptide 1-28 in 40% 2,2,2-trifluoroethanol was investigated by two-dimensional H-1-nmr spectroscopy. All H-1 resonances, except the gamma, delta, and epsilon protons of the lysine residues, could be sequentially assigned. Numerous intraresidual as well as short-range interresidual nuclear Overhauser effect spectroscopy connectivities were observed. Using a variable-target function minimization, a molecular model consisting of two helical stretches involving residues 7-15 and 19-27 connected by a region of undefined structure was calculated. The existence of an undefined structure between residues 16 and 18 confers mobility to the peptide molecule.