Covalent labeling of protein components of the sodium channel with a photoactivable derivative of scorpion toxin.

Azidonitrobenzoyl mono125Iiodo scorpion toxin can be covalently attached to its receptor site in electrically excitable neuroblastoma cells or synaptosomes by photolysis. A polypeptide of Mr approximately 250,000 is specifically labeled in neuroblastoma cells. Labeling is blocked by unlabeled scorpion toxin and by depolarization. This polypeptide is not labeled in a variant neuroblastoma clone lacking voltage-sensitive sodium channels. Polypeptides of Mr approximately 250,000 and Mr approximately 32,000 are specifically labeled in synaptosomes. This labeling is also blocked by unlabeled toxin and by depolarization. These results identify specific polypeptides of Mr approximately 250,000 and Mr approximately 32,000 that are components of the sodium channel.