Abstract
The tetrodotoxin binding component of the voltage-sensitive sodium channel from Electrophorus electricus electroplax was purified by using a monoclonal antibody. An impure preparation of tetrodotoxin binding component was mixed with the pure monoclonal antibody, and the immune complex so formed was isolated by affinity chromatography on a protein A-Sepharose column. Excess antibody was removed by ion-exchange chromatography. The purified material has a specific activity of over 1,800 pmol of [3H]tetrodotoxin bound per mg of protein. By assuming that the immune complex has a stoichiometry of 1:1, this specific activity then represents an actual specific activity of 3,000 pmol of [3H]tetrodotoxin bound per mg of eel electroplax protein, or 75% of the theoretical specific activity expected for a pure toxin binding component of Mr 250,000. The peptide composition of the purified material was simple with the predominant species present being of Mr approximately equal to 250,000. Minor components were also present with Mrs of approximately equal to 95,000, approximately equal to 44,000, and approximately equal to 23,000.