Primary structure of toxin IV of Leiurus quinquestriatus quinquestriatus

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Abstract
We report the sequence of toxin IV of Leiurus quinquestriatus quinquestriatus, one of the five toxins lethal for the mouse purified from the venom of this scorpion. Automatic sequencing of the S‐carboxymethylated protein and derived peptides obtained by action of the Staphylococcus aureus protease allowed us to work out the complete sequence of 65 residues. The toxin which was found to be blocked at the C‐terminal end has an extra residue at the N‐terminus as compared with other toxins from Asian and African scorpions. Moreover, toxin IV must be classified as an α‐scorpion toxin since it was shown to displace competitively 125I‐toxin II of Androctonus australis Hector (125I‐AaH II) from its binding site on rat brain synaptosomes. Nevertheless, it cannot be classified in one of the groups of scorpion toxins previously defined on the level of their antigenic properties. Again the classifications of scorpion toxins based on sequence homologies or antigenic properties support one another.