[Effect of modification of Naja naja oxiana neurotoxin II on the stoichiometry of its complexes with acetylcholine receptor].

It was discovered that illumination of the complex formed by the solubilized acetylcholine receptor from Torpedo marmorata and Lys25-p-azidobenzoyl derivative of neurotoxin II results in the appearance on the receptor of up to 4 additional binding sites. Acetylcholine and neurotoxin II, but not the long-chain neurotoxins bind specifically to these sites. The additional binding sites could be also detected after illuminating the receptor complex with other photoactivable derivatives, provided the latter were displaced from one of the two main binding sites by hexa(trifluoroacetyl)neurotoxin II. A similar, but less pronounced effect, was observed on binding Lys25 (Ac) derivative of neurotoxin II. The formation of the additional binding sites was found to depend on the activity of the receptor preparations as well as on the mutual influence of the two main toxin-binding sites.