Isolation, chemical and biological characterization of margaratensin, a neurotensin-related peptide from the skin of Rana margaratae.

A new neurotensin (NT)-related peptide, margaratensin, was obtained by Sep-Pak C18 and RP-HPLC from methanol extracts of the skin of Chinese frog Rana margaratae. The structure of the peptide has been determined to be Asp-Lys-Arg-Pro-Tyr-Ile-Leu-His-Glu, which is found to be homologous to the COOH-terminal sequence of NT, but has an extra His-Glu at the COOH-terminus. The synthetic preparation was shown to be indistinguishable from the native peptide during HPLC, amino acid analysis and bioassay. Margaratensin exhibited a hypotensive effect in the rat but the response was weaker than NT. The peptide could induce a potent and reproducible contractile activity on GPI which was different from xenopsin, another NT-related peptide from amphibian skin.