No abstract

Taipoxin (taipan toxin), purified from the venom of the Australian taipan (Oxyuranus s. scutellutus) by gel filtration on Sephadex G-75 followed by column zone electrophoresis, is the most lethal neurotoxin yet isolated from any snake venom. The LDso is 2 pg/kg in the mouse. The main physiological effect is a gradual reduction to complete stop of evoked and spontaneous release of acetylcholine from motor nerve terminals. Intoxicated animals die of asphyxia caused by neuromuscular blockage of the respiratory muscles.Taipoxin is a moderately acidic sialo-glycoprotein (pl5) with a molecular weight of 45 600 as calculated from composition data or 46 800 as determined by meniscus depletion sedimentation equilibrium. Taipoxin is a 1 : 1 : 1 ternary complex of subunits designated a, ,O and y which dissociate completely at low pH and high ionic strength or in 6 M guanidine hydrochloride. The dissociation by guanidine at neutral pH is reversible, while the acid-induced dissociation is not. The a and /3 components consist of 120 amino acid residues cross-linked by seven disulfide bridges, whereas the y component has 135 residues and eight disulfides.The very basic (pl > 10) a component contains 13 residues of arginine and is the only subunit displaying lethal neurotoxicity (mouse LDso = 300 pg/kg). The neutral fl fraction was separated by ion-exchange chromatography into two iso-component , fll and 8 2 , which differ slightly in amino acid composition. The very acidic y component contains all of the carbohydrate, which includes 4-5 residues of sialic aid. The three subunits are homologous in sequence although the y component is eight residues longer on the N-terminus and must also contain extra amino acids elsewhere.

No abstract

No abstract

The principal neurotoxins of two commercial (Miami Serpentarium) preparations of venom from Naja naja siamensis, or Thailand cobra, and Naja naja naja, or spectacled Indian cobra, are isolated rapidly and simply by ion exchange chromatography on short (20–30 cm) columns of Bio‐Rex 70 (or IRC‐50) in volatile ammonium acetate buffers, followed by gel filtration on Sephadex G‐50. The Naja naja siamensis preparation contains a single principal neurotoxin that accounts for about one‐fourth of the weight of the lyophilized crude venom, or one‐third of the total venom protein. The Naja naja naja venom preparation contains approximately equal amounts of two principal neurotoxins which together account for more than one‐fourth of the total venom protein. The three principal neurotoxins contain 71 amino acids in a single peptide chain cross‐linked by five disulfide bridges. The two Naja naja naja neurotoxins appear to differ only by a serine/isoleucine substitution, while both appear to differ from the principal Naja naja siamensis toxin only by two additional replacements: arginine for lysine and glycine for alanine. Three minor neurotoxic components that are present at levels of 1% or less in the Naja naja siamensis venom are also described. One of these is a 61 amino acid toxin containing four disulfide bridges and two residues of tryptophan. The other two contain 62 amino acids and four disulfide bridges. One of the latter toxins appears to be nearly identical to the cobrotoxin of Naja naja atra venom.