Pufferfish Saxitoxin and Tetrodotoxin Binding Protein (PSTBP) Analogues in the Blood Plasma of the Pufferfish , , , and .

Pufferfish saxitoxin and tetrodotoxin (TTX) binding protein (PSTBP) is a glycoprotein that we previously isolated from the blood plasma of the pufferfish ; this protein was also detected in seven species of the genus . We proposed that PSTBP is a carrier protein for TTX in pufferfish; however, PSTBP had not yet been found in genera other than . In this study, we investigated the presence of PSTBP-like proteins in the toxic pufferfish , , , and . On the basis of ultrafiltration experiments, TTX was found to be present and partially bound to proteins in the plasma of these pufferfish, and Western blot analyses with anti-PSTBP antibody revealed one or two bands per species. The observed decreases in molecular mass following deglycosylation with glycopeptidase F suggest that these positive proteins are glycoproteins. The molecular masses of the deglycosylated proteins detected in the three species were larger than that of PSTBP in the genus , whereas the two bands detected in had molecular masses similar to that of tributyltin-binding protein-2 (TBT-bp2). The -terminal amino acid sequences of 23⁻29 residues of these detected proteins were all homologous with those of PSTBP and TBT-bp2.