1H-13C selective NOE studies of the decapeptide gramicidin S.

The cyclic decapeptide gramicidin S has been used as a model biopolymer to test the reliability of a structural method which is based on a relaxation analysis of heteronuclear selective NOEs. The observation of through-the-space dipolar couplings between intra- and inter residue amide protons and carbonyl carbons, perfectly consistent with the well established peptide solution conformation, confirms the effectiveness of this structural approach. As a corollary of the latter, carbonyl carbon resonances are unequivocally assigned. Moreover, a direct experimental proof of a Orn-NH2----Phe C = O hydrogen bonding is here given.