Abstract
Two novel toxins containing 66 amino acid residues each were isolated from the venom of the scorpions Centruroides infamatus infamatus and Centruroides limpidus limpidus, respectively. Their full amino acid sequences were determined. Comparison of primary structures showed that they share 97% similarity among themselves and 83% to that of toxin 2 from Centruroides noxius. The three toxins studied compete with each other for the same binding sites on membranes prepared from rat brain synaptosomes, suggesting that they are all β-scorpion toxins. Toxin action was assayed into the μI-2 rat skeletal muscle Na + channel heterologously expressed into Xenopus oocytes. All three toxins block this Na + channel in a similar fashion, without affecting inactivation, and showed IC 50 values in the micromolar concentration range.
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