Identification by cross‐linking of a beta‐bungarotoxin binding polypeptide in chick brain membranes.

beta‐Bungarotoxin (beta‐BTX) is a snake venom neurotoxin which inhibits neurotransmitter release from different types of nerve terminals. To identify presynaptic membrane components potentially important in neurosecretion, 125I‐labeled beta‐BTX (mol. wt. 21 000) was cross‐linked to a high‐affinity binding site in synaptic membrane fractions of chick brain using the photoactivable cross‐linker N‐succinimidyl‐6(4′‐azido‐2′‐nitrophenylamino)‐hexanoate. Electrophoretic analysis of the cross‐linked membrane proteins under both reducing and non‐reducing conditions revealed a single [125I]beta‐BTX‐polypeptide adduct of apparent mol. wt. 116 000 (+/‐ 2000). The labeling of this band was prevented under conditions previously shown to inhibit the binding of [125I]beta‐BTX to its high‐affinity binding site. It is concluded that the cross‐linking procedure identified a polypeptide of the presynaptic binding site for beta‐BTX, and that this polypeptide has a mol. wt. of 95 000.