[14C]chloroacetylcholine as an advantageous affinity label of the acetylcholine receptor

The alkylating agent [14C]chloroacetylcholine perchlorate [( 14C] ClACh) was synthesized and used for affinity labelling of the nicotinic acetylcholine receptor from Torpedo marmorata. Solubilized and affinity-purified receptor proteins were reduced and alkylated according to the bromoacetylcholine-method. Covalent binding of [14C] ClACh to the cholinergic receptor proved to be specific and saturable, and occurred exclusively to the alpha-subunit. Halogen substitution of acetylcholine by chlorine and insertion of a 14C-isotope instead of the widely used 3H resulted in favourable properties of the affinity label.