Purification and properties of a proteinaceous toxin from the brackishwater clam (Corbicula japonica)

Abstract

Water extracts from the brackishwater clam (Corbicula japonica) are lethal to mice upon i.v. injection. Further mouse assays confirmed that the toxicity exhibits a regional variation but no seasonal or sexual variations. The C. japonica toxin was purified from foot muscle, the most toxic tissue, successively by hydrophobic chromatography on Phenyl Sepharose, gel filtration on Sephacryl S-200, hydrophobic FPLC on Phenyl Superose and cation-exchange FPLC on Mono S. The purified toxin had an i.v. LD50 of 11μg/kg against mice. It was a weakly basic protein (pI 7.7) with a mol. wt of 23,000 and was rich in Gly, Glx and Asx but devoid of Met. Analysis of the purified toxin by a protein sequencer afforded no N-terminal amino acid. In addition to C. japonica, two species of freshwater clams belonging to the genus Corbicula, C. leana and C. sandai, were newly found to be toxic, although much less potent than C. japonica. Despite the difference in anatomical distribution of toxins among the three species of Corbicula clams, both C. leana and C. sandai toxins were closely similar in stability and mol. wt to the C. japonica toxin.