Molecular characteristics of four new depressant insect neurotoxins purified from venom of Buthus martensi Karsch by HPLC.

Suitable pattern and high yield were obtained when the reverse-phase performance liquid chromatography (RP-HPLC) was used to separate neurotoxins from venom of Chinese scorpion Buthus martensi Karsch. Using this technique, the venom was first separated to two main regions. The toxicity tests show that the insect-selective neurotoxical components are concentrated in the latter region, from which five insect-selective neurotoxins designated by BmK IT1-IT5 were obtained. According to the results of the toxicity test as well as the amino acid composition and N-terminal analyses, BmK IT1 is the excitatory insect neurotoxin as reported in a previous paper, and the others are the newly found depressant insect-selective neurotoxins. The molecules of all the four toxins are single-chain minipeptides of about 60 amino acids. Their isoelectric points (pI) are between 8.3 and 8.5. The fact that BmK IT2 loses completely its insect toxicity after being modified by fluorochrome shows that the positive charges on the molecular surface of this kind of toxins are important to maintaining the bioactivity of the molecules.