Isolation and structure of ranamargarin, a new tachykinin from the skin of Chinese frog Rana margaratae.

A new tetradecapeptide, ranamargarin, has been isolated by Sep-Pak C18 and HPLC from methanol extracts of the skin of the Chinese frog Rana margaratae. The sequence of the peptide is: Asp-Asp-Ala-Ser-Asp-Arg-Ala-Lys-Lys-Phe-Tyr-Gly-Leu-Met-NH2. This structure has been confirmed by synthesis. The peptide is the largest among the amphibian tachykinins and its N-terminal amino acids are quite different from those of the other tachykinins. The formation of the sulfoxide and peak-splitting of ranamargarin during purification procedures are briefly discussed.