Ligand binding to the nicotinic acetylcholine receptor is studied by surface plasmon resonance. Biotinylated bungarotoxin, immobilized on a streptavidin-coated gold film, binds nicotinic acetylcholine receptor both in detergent-solubilized and in lipid vesicle-reconstituted form with high specificity. In the latter case, nonspecific binding to the sensor surface is significantly reduced by reconstituting the receptor into poly(ethylene glycol)-lipid-contg. sterically stabilized vesicles. By preincubation of a bulk nicotinic acetylcholine receptor sample with the competing ligands carbamoylcholine and decamethonium bromide, the subsequent specific binding of the receptor to the surface-immobilized bungarotoxin is reduced, depending on the concn. of competing ligand. This competition assay allows the detn. of the dissocn. consts. of the acetylcholine receptor-carbamoylcholine complex. A KD = 3.5 * 10-6 M for the detergent-solubilized receptor and a KD = 1.4 * 10-5 M for the lipid vesicle-reconstituted receptor are obtained. For decamethonium bromide, a KD = 4.5 * 10-5 M is detd. for the detergent-solubilized receptor. This approach is of general importance for investigating ligand-receptor interactions in case of small ligand mols. by mass-sensitive techniques. [on SciFinder (R)]