15N spin-lattice relaxation study of linear peptides: Preliminary results on Leu-enkephalin and Tyr-Gly-Gly-Phe

The ability of 15N relaxation measurements in conformational analysis of linear peptides was studied using Leu-enkephalin: Tyr-★Gly-★Gly-★Phe-★Leu and and related tetrapeptide Tyr-★Gly-★Gly-★Phe 95 % 15N enriched. 15N spin-lattice relaxation times measured at different temperatures in Me 2SO solution indicate the presence of highly preferential folded structures in both peptides. A marked dependence of T 1 upon the motional effects (segmental rather than anisotropic overall) was observed, while hydrogen bonding affects weakly the relaxation times. From a comparison of 15N relaxation parameters it appears that the tetrapeptide exhibits a more rigid structure than Leu-enkephalin, in accordance with previous 1H NMR studies. This paper provides evidence for the usefulness of 15N T 1 as a mobility probe (independent from 13C) in the investigation of the conformational dynamics of peptides.