Isolation of the Principal Neurotoxins of Two Naja naja Subspecies

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.