ABSTRACT
A study was carried on the mode of action and some properties of a cobra neurotoxin inhibitor found in the extract of Curcuma sp. (Zingiberaceae). When the principal postsynaptic neurotoxin (STX) of the Thai cobra (Naja naja siamensis) was mixed with an aqueous extract of Curcuma sp. rhizome, the STX was inactivated as tested in mice or in vitro using a rat hemidiaphragm preparation. The 'neurotoxin inhibitor' ('NTxI') was found only in the water insoluble fraction of the rhizome extract. Using radioactively labeled neurotoxins, 125I-STX and 3H-STX, it was demonstrated that the neurotoxin did not form a stable complex with the 'NTxI'; the inactivated neurotoxin remained in the supernatant of the reaction mixture. After inactivation by 'NTxI', the STX exhibited an unchanged molecular weight as judged by SDS-polyacrylamide gel electrophoresis and an unchanged isoelectric point in isoelectric focusing. Extraction of the Curcuma sp. rhizome with at least 0.2% Triton X-100 resulted in solubilization of a component capable of forming a soluble and stable complex with 3H-STX. By column chromatography on Sephadex G-200 in the presence of 0.1% Triton X-100, the toxin-binding compound was shown to have a molecular weight of about 150 kDa. This 150 kDa component was obtained by Triton extraction of the water-insoluble fraction, and much less from the water soluble fraction, of Curcuma sp. rhizome. It did not possess any carbohydrate side-chain capable of binding the lectin Concanavalin A. The time course of the 150 kDa-3H-STX complex formation was extremely slow (approx 22 hours).(ABSTRACT TRUNCATED AT 250 WORDS)