Isolation of dermenkephalin from amphibian skin, a high‐affinity (δ‐selective opioid heptapeptide containing a D‐amino acid residue

Abstract

The predicted amino acid sequence of the biosynthetic precursor of dermorphin, a highly potent and nearly specific μ-opioid peptide from amphibian skin, contains four repeats of the dermorphin progenitor sequence and one single copy of a different heptapeptide sequence. We have developed a specific enzyme immunoassay and used synthetic peptides to detect and purify the new predicted heptapeptide 2.4 μg/g dry skin) from the skin of the Phyllomedusa sauvagei frog from which dermorphin was originally isolated. The identity of the novel pro-dermorphin related peptide, Tyr-D-Met-Phe-His-Leu-Met-Asp-NH₂, was established by co-chromatography with synthetic peptides on reverse-phase HPLC, immunological analysis, gas-phase sequencing, mass spectrometry and by pharmacological assays. Opioid-binding assays in vitro demonstrated that both the natural and synthetic heptapeptides displayed exceptionally high selectivity and affinity towards the δ-opioid receptors. Because of its origin and its δ-opioid (enkephalin) activity and specificity, this novel D-amino acid containing peptide is named dermenkephalin.