A substance with immunoreactivity to the peptide physalaemin in mammalian respiratory tissue

Physalaemin (Mr = 1284) is a potent undecapeptide from the skin of South American frogs. The amino acid sequence of the COOH-terminal region of this peptide is similar to that of substance P. An antiserum specific for the NH2-terminal sequence of physalaemin enabled the quantitation and localization of physalaemin-like immunoreactivity (PSLI) in mammalian tissues. PSLI is found in acid extracts of whole trachea from rat, rabbit, and guinea pig and in the tracheal mucosal layer in the dog, cow, and pig. The concentration determined by radioimmunoassay ranged from 1 to 15 ng/g dry weight of tissue, with rat trachea containing the highest amount. Gel filtration of an extract of rabbit trachea on Bio-Gel P-4 revealed a single peak of immunoreactivity that had an approximate Mr of 1700, similar to that detected in extracts of guinea pig and rabbit stomach. In contrast to amphibian physalaemin, mammalian PSLI 1) has a higher molecular weight, 2) is resistant to alpha-chymotrypsin or trypsin digestion, 3) elutes earlier from a C18 alkylsilane resin with increasing concentrations of methanol, and 4) can be separated from physalaemin by thin-layer chromatography. These data indicate that the mammalian PSLI is different in structure from the amphibian peptide.