Bot IT2: a new scorpion toxin to study receptor site on insect sodium channels.

The insect-specific Bothus occitanus tunetanus IT2 toxin is distinguishable from other scorpion toxins by its amino acid sequence and effects on sodium conductance. The present study reveals that Bot IT2 possesses in cockroach neuronal membranes a single class of high affinity (Kd = 0.3 +/- 0.1 nM) and low capacity (Bmax = 2.4 +/- 0.5 pmol/mg) binding sites. Competitive binding experiments with several known sodium channel neurotoxins reveal that the Bot IT2 binding site is in close proximity to the other toxins.