α-bungarotoxin, labeled with 125I on tyrosine residue 54. α-bungarotoxin is a snake venom neurotoxin that acts as an antagonist at nicotinic acetylcholine receptors (nAChRs). This product as offered at two specific activities. Specific activity indicates how much radioactivity there is per molecule of ligand. Several of our 125I-labeled ligands are offered at maximum specific activity (2200 Ci/mmol if one 125I labeling site is available). This indicates that virtually every molecule of ligand provided in the stock vial is radiolabeled.