Intramolecular microdynamical and conformational parameters of peptides from proton and ¹³C NMR spin-lattice relaxation. Tetragastrin

Abstract

Measurements of 1H and 13C spin-lattice relaxation and 13C nuclear Overhauser enhancement factors are reported for dimethyl sulfoxide solutions of tetragastrin, a pharmacologically active tetrapeptide. The use of the dipolar formalism for predicting 1H and quaternary 13C relaxation rates is discussed. Furthermore, the prospect is opened for the use of quaternary 13C and 1H relaxation times to obtain information on the peptide torsion angles phi, psi, and chi in a way supplementing NMR coupling constant methods presently in use.

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

“…Moreover, the NT1 values of Phe4 a, (3, and r in D20 agree within experimental error, indicating that appreciable reorientation about the Ca-C, bond is absent in this solvent. In Me2SO-d6 the slightly longer T, of Phe4 {as compared to Phe4 a parallels the situation found for tetragastrin (13) and indicates some motional freedom of the C-Cr axis. In the Tyr' residue the aromatic ring, contrasting with that of Phe4, exhibits no reorientation about its C7-Cr axis on a time scale rapid compared to that defined by overall molecular tumbling.…”

Definitive assignment of 13C NMR signals in tryptophan and related molecules

“…More recently, data derived for C-13 enriched tryptophan (C3) [6] and INDO calculations [7] were published. It should be noted that the order of increasing chemical shifts for C-4, C-5 and C-6 culled from published data are widespread, as shown by the following sets: C4 < C5 < C6 [15], C6 < C5 < C4 [2,14], C6 < C4 < C5 [8], in perdeuterodimethyl sulfoxide; C4 < C5 < C6 [6], C4 < C6 < C5 [4,9], C6 < C5 < C4 [2,12] in deuterium oxide; C4 < C5 < C6 [7] in water and C4 < C5 < C6 [5,13,15] in deuterochloroform. Similarly, for 5-hydroxyindole and derivatives [7, an analogous situation is recognized for the signal owing to carbons 4 and 6.…”

A study of proton relaxation mechanisms, stereochemistry, and dynamics of the decapeptide tyrocidine A

“…Each amide proton, NH(i'), is relaxed primarily by the Ha(z') and ( -1), by the ß protons of the zth and (z -l)th residues, and by transannular protons similar to the Ha(2)-Ha(7) effects discovered by NOE difference spectroscopy. 18 In general we can write the following additivity relationship for an a or amide proton: R'(i) = /?</, + R¿ + Rx + Ro + Rta where is the interaction between the a and NH protons in the same residue, R¿ is the interaction between NH(z') and a(i - 1) protons, Rx is the interaction between an a or NH proton and the side-chain protons, Rja is the transannular interaction, and R0 is the relaxation rate due to mechanisms other than proton-proton dipolar relaxation. For a rigid backbone terms R and R^w ill depend only on the correlation time for the overall motion of the molecule and on the distances or , respectively.…”