Physalaemin: an amphibian tachykinin in human lung small-cell carcinoma

Immunoreactivity to the amphibian peptide physalaemin was characterized from extracts of a human lung small-cell carcinoma by immunological, chemical, and pharmacological means. Tumor-related peptide cross-reacted with three antiserums to physalaemin to yield 1.1 to 1.6 nanomoles per gram of tissue. Physalaemin and tumor peptide had similar retention times on high-performance liquid chromatography after chemical and enzymic modifications that included pH changes, oxone oxidation, use of a hydrophilic ion-pairing reagent, and digestion with trypsin and pyroglutamate aminopeptidase. Both physalaemin and the tumor peptide produced a contractile response of isolated guinea pig ileum at threshold concentrations of approximately 100 to 150 picograms per milliliter. These data suggest that small-cell carcinoma of the lung contains a physalaemin-like peptide that has structural and biological homology to its amphibian counterpart.