Purification of a presynaptic neurotoxin from the venom of the Australian tiger snake Notechis scutatus scutatus

Abstract

The venom of the Australian tiger snake Notechis scutatus scutatus has been fractionated by ion-exchange chromatography on Bio-Rex 70 in an ammonium acetate gradient. The main neurotoxic component, the notexin, which constituted 6 per cent of the crude venom, was thereby obtained in a high degree of purity (⩾97 per cent) in one purification step. It is a basic protein of 119 amino acid residues in a single peptide chain cross-linked by seven disulfide bridges. The formula weight is 13,574. The LD 100 is 25 μg/kg mouse. The toxin causes dyspnea and paralysis of the hind legs and in the final stages before death, the mice lie immobilized. The death follows two to three days after the administration of a lethal dose. The notexin is a presynaptic toxin which inhibits the release of acetylcholine from motor nerves. The tiger snake venom also contained four other highly active toxins, three of which were submitted to a preliminary study. The first of these toxins has about 60 amino acid residues and an LD 100 of 100 μg/kg mouse, and the second has about 70 residues and an LD 100 of 150 μg. Both toxins have probably a postsynaptic mode of action, as they appear to have all characteristics in common with the postsynaptic cobra ( Naja naja) neurotoxins. The third toxin, which contains about 120 residues and has an LD 100 of 600 μg, causes respiratory distress characteristic for a postsynaptic neurotoxin. Sublethal doses can give rise to difficulty in breathing lasting for as long as 48 hr. It resembles the dimers formed during the freeze-drying of cobra neurotoxins. These dimers also cause dyspnea lasting for a long period, whereas the corresponding time for the monomeric cobra toxins is maximally 6 hr.