We previously purified and characterized a peptide toxin, birtoxin, from the South African scorpion Parabuthus transvaalicus. Birtoxin is a 58-residue, long chain neurotoxin that has a unique three disulfide-bridged structure. Here we report the isolation and characterization of ikitoxin, a pep-tide toxin with a single residue difference, and a markedly reducedbiological activity, frombirtoxin. Bioassays onmice showed that high doses of ikitoxin induce unprovoked jumps, whereas birtoxin induces jumps at a 1000-fold lower concentration. .
