Purification and properties of a presynaptically acting neurotoxin, mandaratoxin, from hornet (Vespa mandarinia).

A hornet (Vespa mandarinia) neurotoxin, mandaratoxin (MDTX), was purified by simple procedures with column chromatography made on Sephadex G-50 and CM-Sephadex by using an acetate buffer. The molecular weight of homogeneous MDTX was calculated to be approximately 20000 by gel filtration, NaDodSO4 disc gel electrophoresis, and amino acid analysis. MDTX is a single-chain polypeptide. MDTX did not migrate electrophoretically in a basic buffer at pH 8.3 but did so when the buffer was acidic, at pH 4.3. The isoelectric point of the toxin was determined at 9.1 by isoelectric focusing. A relatively high amount of lysine was found in the amino acid analysis. A280nm1% was 15.1. Glucosamine and galactosamine were not detectable by amino acid analysis. MDTX had neither hemolytic nor enzymatic activity. The toxin was heat labile. By use of neuromuscular junctions of a lobster walking leg, it was found that the nanomole range of MDTX irreversibly blocked the excitatory postsynaptic potential without appreciable change in the resting conductance of the postsynaptic membrane. Intracellular recording from the presynaptic nerve fiber showed that MDTX blocked the action potential mainly by reducing the sodium current.