Molecular weight estimates of insect cholinergic receptors by radiation inactivation

Molecular weight (MW) estimates for sites to which the radiolabelled cholinergic receptor probes alpha-bungarotoxin and N-methylscopolamine bind in CNS extracts of the cockroach Periplaneta americana have been made by radiation inactivation analysis. The MW of 77,600 determined for [3H]N-methylscopolamine binding sites agrees well with published values for vertebrate muscarinic acetylcholine receptor sites. In contrast, N-[propionyl-3H]propionylated alpha-bungarotoxin binds to a separate membrane component of lower MW (108,000) than previously reported values for vertebrate and insect nicotinic acetylcholine receptors. This appears to represent one or more subunits of the receptor complex, containing the recognition site.