Subunit Structure of α‐Bungarotoxin Binding Component in Mouse Brain

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Abstract
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 1 major and 1 minor band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The MW 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 analyzed by cross-linking followed by SDS-PAGE. The results fitted the model for an .alpha.-bungarotoxin binding component in the mouse brain composed of 6 identical or very similar subunits of 51,000-52,000. One subunit carrying the binding site for toxin bound 1 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.