NEUROTOXIN-MODULATED UPTAKE OF SODIUM BY HIGHLY PURIFIED PREPARATIONS OF THE ELECTROPLAX TETRODOTOXIN-BINDING GLYCOPEPTIDE RECONSTITUTED INTO LIPID VESICLES

Using the dialysable detergent CHAPS (3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate), the tetrodotoxin-binding protein from the electoplax of the electric eel has been purified to a high degree of both chemical homogeneity and toxin-binding activity. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the best preparations showed only a single microheterogeneous band at Mr approximately 260,000, despite attempts to visualize smaller bands by sample overloading. Upon dialysis, this material became incorporated into the membranes of small unilamellar vesicles, and in this form the purified protein exhibited tetrodotoxin-binding properites similar to the component in the original electroplax membrane. Furthermore, in the presence of activator neurotoxins the vesicles were able to accumuate isotopic sodium in a manner similar to that previously decribed for less active or less pure preparations of vesicles containing either mammalian or eel electroplax toxin-binding protiens. Quantitative consideratioin of the isotopic transport activity of this pure material, along with the high degree of purity of the protein, strongly suggests that the 260-kDa glycopeptide electroplax is necessary and sufficient to account for the sodium channel function seen in these studies, and eliminates the possible involvement of smaller peptides in the channel phenomena observed.