A major lethal factor of the venom of Burmese Russell's viper (Daboia russelli siamensis): isolation, N-terminal sequencing and biological activities of daboiatoxin.

A major lethal factor, daboiatoxin (DbTx), showing strong PLA2 activity (specific activity 91.7 nmoles/min/mg), was purified to homogeneity from the venom of Burmese Russell's viper (Daboia r. siamensis) by a combination of gel filtration on Sephadex G-75 and ion-exchange chromatography on CM-Sephadex C-25, followed by purification on high-performance gel filtration Shim-pack Diol-150 column. DbTx is a single-chain PLA2 toxin with approximate mol. wt 15,000 as determined by HPLC gel filtration and SDS-PAGE. It constitutes 12% of total venom protein and is the main lethal component of Burmese Russell's viper venom with an LD50 i.p. (0.05 mg/kg) 12-fold greater than that of the whole venom (LD50 i.p. 0.6 mg/kg). DbTx produces neurotoxic symptoms in mice and exhibits potent oedema-inducing activity (minimum oedema dose 0.05 microgram), indirect haemolytic activity and a strong myonecrotic activity, but no haemorrhagic activity. DbTx is cytotoxic to HeLa cells causing cytolysis of the cells 24 hr post-exposure to toxin (50 micrograms/ml). The first 20 N-terminal amino acid sequence (NFFQF AEMIV KMTGK EAVHS) shows a significant resemblance to those of the PLA2s from the venoms of Bulgarian viper (V. a. ammodytes) and Taiwan Russell's viper (V. r. formosensis).