Preliminary analysis of 1H and 13C spectral and relaxation behavior in methionine-enkephalin.

Nuclear magnetic resonance studies on the conformational dynamics of the pentapeptide H-Tyr-Gly-Gly-Phe-Met-OH are reported. This peptide, for which the generic trivial name "methionine-enkephalin" has been suggested, is pharmacologically active as a ligand for the mammalian opiate receptor(s). The studies reported are parallel investigations in two solvents (dimethylsulfoxide and water) of: 1H and 13C high resolution spectral assignments; 1H and 13C spin-lattice relaxation times, temperature dependence of amide proton chemical shifts, and half-times for chemical exchange or amide protons. From these data we conclude that the tyrosine side chain of methionine-enkephalin exhibits restricted motion with respect to the main peptide backbone of the molecule. On the other hand both the phenylalanyl and methionyl side chains are undergoing intramolecular reorientation with relatively high frequency.