[D-LEU(2)]DELTORPHIN, A 17 AMINO-ACID OPIOID PEPTIDE FROM THE SKIN OFTHE BRAZILIAN HYLID FROG, PHYLLOMEDUSA-BURMEISTERI

A novel 17 amino acid peptide, having a D-leucine in position 2 of its sequence, has been isolated from methanol extracts of the skin of the Brazilian frog, Phyllomedusa burmeisteri. The sequence of the peptide is: l-Ala-Ser-Thr-Ile-Gly-Asp-Phe-Phe-His-Ser-Ile-NH2. It displays a poor affinity for delta-opioid binding sites, both in the periphery an d in the central nervous system. However, the shorter synthetic amidat ed analogue (1-10) possesses both on the central and peripheral delta binding sites an agonistic potency equalling in affinity and exceeding in selectivity that of the enkephalins. The shorter amidated analogue (1-7) is virtually inactive on opioid binding sites in the periphery, but displays a clear-cut affinity for both delta and mu binding sites on rat brain membranes. To date six different D-amino acid residues h ave been found, always in position 2 of the sequence, in as many as 11 natural peptide molecules of animal origin.