Affinity directed crosslinking of acetylcholine receptor polypeptide components in post−synaptic membranes

A photolabile derivative of α−bungarotoxin which binds specifically to Image acetylcholine receptor has been used to investigate the topography of the membrane associated protein. It is shown that the toxin can be crosslinked to a polypeptide of 40,000 daltons, to which it is known to bind, and in addition to another polypeptide of 65,000 daltons which is a major constituent of the membrane. The results substantiate the notion that this nicotinic acetylcholine receptor is composed of different polypeptides and that some of these interact with each other or are in close proximity on the exterior surface of the post−synaptic membran