Subunit structure of alpha-bungarotoxin binding component in mouse brain.

The alpha-bungarotoxin binding component in mouse brain was purified by affinity chromatography with toxin-Sepharose, gel-chromatography on Sepharose 6B, and ion-exchange chromatography with DE52 resin. The iodinated product of the last step produced one major and one minor band on sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The molecular weight of the minor peak was twice as large as that of the major one. The iodinated product could bind alpha-bungarotoxin, and this binding was inhibited by a nicotinic antagonist, d-tubocurarine, which demonstrated that the iodinated product was a true alpha-bungarotoxin binding component. The molecular structure of the product was analysed by cross-linking followed by SDS-PAGE. The results fitted the model for an alpha-bungarotoxin binding component in the mouse brain composed of six identical or very similar subunits of 51,000--52,000. One subunit carrying the binding site for toxin bound one molecule of toxin. This subunit structure of an alpha-bungarotoxin binding component in the brain is discussed in comparison with that of a nicotinic acetylcholine receptor in the electric organ.