Properties of an alpha-bungarotoxin-binding cholinergic nicotinic receptor from Drosophila melanogaster.

alpha-[125I]Bungarotoxin specifically binds to homogenates of Drosophila melanogaster head at levels of 0.3-0.8 pmol/mg protein. The dissociation constant calculated from rates of association and dissociation of toxin.receptor complex, is 0.6.10(-9) M. Ca2+, and to a lesser extent Na+, inhibit the reaction. alpha-[125I]Bungarotoxin binding is inhibited by low concentrations of unlabelled toxin, nicotinic ligands and eserine, but not by low concentrations of muscarinic ligands, decamethonium or an organophosphate. The receptor is membrane bound and can be partially released into 100 000 X g supernatant by combination of 1 M NaCl and 1% Triton X-100. Most of the activity in the supernatant sediments after further centrifugation at 200 000 X g for 2 h. Toxin binding sites are distinct from acetylcholinesterase molecules as revealed by pharmacological, biochemical and genetic techniques. The gene for the toxin-binding nicotinic receptor in Drosophila is apparently not located adjacent to the gene for acetylcholinesterase.