The resonances of the Cαand Cβprotons of the cystyl. asparaginyl, and aromatic residues of [8-arginine]vasopressin (AVP) in D2O at pD 3.8 and 20°C were assigned in a rigorous manner by the use of isotopic isomers of AVP that contain specific replacements of protons by deuterons and by comparison of1H NMR characteristics of AVP to those of [8-lysine]vasopressin (l.VP) and oxytocin (OT). Although there is extensive overlap of resonances of Cβprotons even at 360 MHz, all of the chemical shifts of these protons and most of the couplings between them and their vicinal C protons could be determined, at least to a first approximation. It was concluded that the cyclic moieties (residues 1-6) of AVP, LVP, and OT possess essentially the same overall backbone conformation, and that the side-chain conformation-or rotamer populations-about the Oα-Cβbonds of the cystyl residue (positions 1 and 6). the tyrosyl residue (position 2), and the asparaginyl residue (position 5) are similar. This study indicates that selective replacements of Cβprotons by deuterons are necessary to improve the accuracy of coupling constants extracted from 360-MHz spectra of AVP for use in conformational analysis.
ASJC Scopus subject areas
- Colloid and Surface Chemistry