Purification and Properties of a Proteinaceous Toxin Newly Found in the Roe of Lamprey Lampetra japonica

Abstract

The aqueous extract from the mature roe (gonad index > 10%) of the lamprey Lampetra japonica was found to be lethal to mice when injected intravenously, while that from the immature roe (gonad index about 4%) was nontoxic. Dinogunellin, the well-known fish roe toxin, was not detected in the lamprey roe. The lamprey toxin was a thermolabile, basic protein and purified to an electrophoretically pure state from the mature roe by chromatography on CM-cellulose and hydroxyapatite, FPLC on Mono S, and HPLC on TSKgel Ether-5PW. The purified toxin was highly lethal to mice upon intravenous injection; its LD50 was estimated to be 13 μg/kg. Analyses by SDS-PAGE either with or without a reducing agent showed that the toxin has a molecular mass of 36 kDa composed of two kinds of subunits with molecular masses of 28 and 10 kDa. The amino acid composition of the toxin was characterized by the abundance of Ser, Glx, and Gly and the scarcity of half-Cys.