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Neurotoxin-modulated uptake of sodium by highly purified preparations of the electroplax tetrodotoxin-binding glycopeptide reconstituted into lipid vesicles
Authors:Daniel S Duch  S Rock Levinson
Institution:(1) Department of Physiology, University of Colorado Medical School, 80262 Denver, Colorado;(2) Present address: Department of Anesthesiology, Cornell University Medical College, 10021 New York, New York
Abstract:Summary Using the dialysable detergent CHAPS (3-(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate), the tetrodotoxin-binding protein from the electroplax 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 atM r 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 properties similar to the component in the original electroplax membrane. Furthermore, in the presence of activator neurotoxins the vesicles were able to accumulate isotopic sodium in a manner similar to that previously described for less active or less pure preparations of vesicles containing either mammalian or eel electroplax toxinbinding proteins. Quantitative consideration 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 from 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.
Keywords:sodium channels  reconstitution  polypeptide composition  lipid vesicles  isotopic fluxes
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