Fig. 1. Affinity labeling of membrane bound receptor with the 4-azidobenzoimidate derivative of ¹²⁵I-α-bungarotoxin.

Membranes prepared from Drosophila heads were preincubated for 20 min with the ligands α-bungarotoxin (Bgtx), κ-toxin, α-cobratoxin (Cbtx), Ach, and nicotine (Nic) at the concentrations indicated. Affinity labeling was carried out with the 4-azidobenzoimidate derivative of ¹²⁵I-α-bungarotoxin. After affinity labeling membranes were collected by centrifugation and subjected to SDS-polyacrylamide gel electrophoresis using a 10% polyacrylamide gel. An autoradiogram of the dried gel is shown. Cross-linking with α-bungarotoxin increases the molecular mass of each band by about 8 kDa.