Sequence and electrophysiological characterization of two insect-selective excitatory toxins from the venom of the Chinese scorpion Buthus martensi.

The two insecticidal peptides Bm32-VI and Bm33-I, isolated from the venom of the Chinese scorpion Buthus martensi induce paralytical symptoms typical of insect contractive toxins. They show, respectively, 74% and 77% homology with AaIT from Androctonus australis, comparable insecticidal activity and no vertebrate toxicity. Under voltage-clamp conditions, both toxins induced (1) an increased fast Na(+) current, (2) a shift in voltage dependence of Na(+) current activation, (3) the occurrence of a delayed current, and (4) a slow development of a holding current. Increased Na(+) conductance at negative potential values is responsible for axonal hyperexcitability and the contractive paralysis of insect prey.