Pufferfish Saxitoxin and Tetrodotoxin Binding Protein (PSTBP) Analogues in the Blood Plasma of the Pufferfish Arothron nigropunctatus, A. hispidus, A. manilensis, and Chelonodon patoca.

Pufferfish saxitoxin and tetrodotoxin (TTX) binding protein (PSTBP) is a glycoprotein that we previously isolated from the blood plasma of the pufferfish Takifugu pardalis; this protein was also detected in seven species of the genus Takifugu. We proposed that PSTBP is a carrier protein for TTX in pufferfish; however, PSTBP had not yet been found in genera other than Takifugu. In this study, we investigated the presence of PSTBP-like proteins in the toxic pufferfish Arothron nigropunctatus, A. hispidus, A. manilensis, and Chelonodon patoca. 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 Arothron species were larger than that of PSTBP in the genus Takifugu, whereas the two bands detected in C. patoca had molecular masses similar to that of tributyltin-binding protein-2 (TBT-bp2). The N-terminal amino acid sequences of 23⁻29 residues of these detected proteins were all homologous with those of PSTBP and TBT-bp2.