Studies on biologically active proteinaceous substances contained in the skin mucus of the Japanese eel

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1. Extracts of the skin mucus of the Japanese eel Anguilla japonica were found to be highly lethal to mice when administered intravenously. The toxin was an acidic protein with a molecular weight of 400000 and was comprised of two types of subunits with molecular weights of 230000 and 110000. Gly and Ala were abundant in the toxin while Met, Cys, Tyr and Trp were very poor. The LD_<50> (i. v. injection into mice) of the purified toxin was estimated to be as low as 3.1 mug/kg.2. At least two lectins, both of which were specific to galactose-related sugars, were detected in the skin mucus of A. japonica. One of them was purified and assumed to be an acidic protein with a molecular weight of 40000-50000. Hemolysins were also contained in the skin mucus but their purification was unsuccessful due to instability.3. A proteinaceous toxin was purified from the serum of A. japonica. The purified toxin had an i. v. LD_<50> of 670 mug/kg and a molecular weight of 150000. Since no neutralization of the serum toxin was exhibited by the antiserum raised against the skin toxin of A. japonica, both toxins were immunologically distinguishable from each other.4. The presence of toxins in the skin mucus was newly established in the following fish : European eel Anguilla anguilla, pike eel Muraenesox cinereus, conger eel Conger myriaster, loach Misgurnus anguillicaudatus, sculpin Cottus pollux and two species of puffer, Takifugu niphobles and Canthigaster rivulata. The toxins of A. anguilla and M. cinereus were chemically and immunologically similar to that of A. japonica.