We have performed an extensive 15N NMR study in water of the peptide hormone oxytocin and of L-prolyl-L-leucyi-glycinamide, the peptide with the sequence of the C-terminal tripeptide of oxytocin. The chemical shifts of all nitrogen nuclei in the two peptides have been determined. These shifts are shown to be very similar to those of N’-acetylamino acids in dimethyl sulfoxide. Deviation from this correlation may be related to conformational restrictions or lack of exposure to solvent. Spinlattice relaxation times (T1i's), nuclear Overhauser enhancements (NOEs), and one-bond N-H coupling constants are reported. Dipolar relaxation dominates the observed T1's, and the ’ 15N relaxation measurements are consistent with isotropic motion of the tocin ring with a correlation time similar to that determined previously from 13C NMR measurements. Paramagnetic metal ions can be particularly troublesome in such 15N studies, and a technique for their removal is described.
ASJC Scopus subject areas
- Colloid and Surface Chemistry