CONFORMATIONAL STUDIES ON ANALOGS OF THE INVERTEBRATE PEPTIDE PYROGLU-ASP-PRO-PHE-LEU-ARG-PHE-NH2 USING H-1-NMR

The peptide pQDPFLRFamide is one of several closely related heptapepti des found in invertebrates, including molluscs. Electrophysiological f indings and ligand binding studies have both suggested that these hept apeptides probably interact with receptors distinct from those that ar e activated by the related tetrapeptide FMRFamide (also found in the s ame group of invertebrates), despite the fact that some synthetic N-te rminally extended analogues of the latter show marked tetrapeptide-lik e activity. We have carried out structural studies, using 1- and 2-dim ensional H-1 NMR, on pQDPFLRFamide and some synthetic analogues in whi ch Asp-2 was replaced by Asn and Pro-3 by either Aib (alpha-amino isob utyric acid) or by Gly. The results are consistent with the suggestion that pQDPFLRFamide can adopt a bent conformation, which might form th e basis of the selectivity of this and related heptapeptides.