Alpha toxins bind voltage-independently at site-3 of sodium channels (Nav) and inhibit the inactivation of the activated channels, thereby blocking neuronal transmission. The dissociation is voltage-dependent. This toxin is active on insects. It is also highly toxic to crustaceans and has a measurable but low toxicity to mice. Expressed by the venom gland. Has the structural arrangement of an alpha-helix connected to antiparallel beta-sheets by disulfide bonds (CS-alpha/beta). LD(50) is 250 ug/kg by subcutaneous injection to mice. The binding sites for this contractive toxin differ from those shared by the excitatory and depressant insect toxins. Belongs to the long (4 C-C) scorpion toxin superfamily. Sodium channel inhibitor family. Alpha subfamily. The mutagenesis studies described in PubMed:8756487 and PubMed:9169449 are made with the sequence from PubMed:2383565 (see the sequence conflict in position 83-85).