Amino acid sequence of the Anthopleura xanthogrammica heart stimulant, anthopleurin A

A highly potent heart stimulant, anthopleurin A, from Anthopleura xanthogrammica was shown to exist as a single polypeptide chain consisting of 49 amino acid residues. The sequence of the peptide was shown to be: Gly-Val-Ser-Cys-Leu-Cys-Asp-Ser-Asp-Gly-Pro-Ser-Val-Arg-Gly-Asn-Thr-Leu-Ser-Gly-Thr-Leu-Trp-Leu-Tyr-Pro-Ser-Gly-Cys-Pro-Ser-Gly-Trp-His-Asn-Cys-Lys-Ala-His-Gly-Pro-Thr-Ile-Gly-Trp-Cys-Cys-Lys-Gln as judged by Edman degradation of the carboxymethylcysteine derivative and the tryptic peptides obtained from the derivative. Although six carboxymethylcysteine residues were present in the polypeptide, no cysteine residues were detectable in the native protein, indicating that there are three cystine residues in anthopleurin A.