SYNTHESIS AND CHARACTERIZATION OF AN N-TERMINAL-SPECIFIC I-125 PHOTOAFFINITY DERIVATIVE OF MU-CONOTOXIN GIIIA WHICH BINDS TO THE VOLTAGE-DEPENDENT SODIUM-CHANNEL

An N-terminal, iodinatable photoaffinity derivative of μ-Conotoxin GIIIA, 4-Azido-salicylyl-μ-Conotoxin GIIIA (CTXASA), was synthesized by solid phase peptide synthesis. The binding of 125I-CTXASA to the voltage dependent sodium channel from electroplax of Electrophorus electricus was specific, as demonstrated by saturation binding experiments. Using autoradiography, 125I-CTXASA labeled a protein with a molecular mass of 260 kDa, consistent with the apparent molecular mass of the sodium channel. This labeling could be suppressed by excess of tetrodotoxin and μ-Conotoxin GIIIA. © 1990.