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Published January 1, 1981 | public
Journal Article Open

Diphtheria toxin forms transmembrane channels in planar lipid bilayers


When exposed to a lipid bilayer, diphtheria toxin binds to it and forms transmembrane, voltage-dependent, anion-selective channels. The mean (± SD) conductance of these channels in asolectin membranes is 6.2± 0.7 pmho (pS) in 0.2 M NaCl and 20± 2 pmho in 1.0 M NaCl. The rate of channel formation depends on the pH in the toxin-containing compartment; it is very low at pH >5.0 and increases abruptly as the pH decreases from 4.9 to 4.0. Binding of toxin to the membrane is also pH dependent, being unmeasurable at pH 7 and increasing monotonically with decreasing pH. The rate of channel formation depends upon membrane potential as well; channels form only at negative potentials. These channels are permanent in the time scale of the experiments (about 1 hr). The membrane conductance caused by the channels is also voltage dependent, being constant at positive potentials and decreasing at negative potentials. Hence, the current-voltage curve is linear at positive potentials and sublinear at negative potentials. The conditions necessary for insertion of toxin into the bilayer and formation of channels are similar to those that prevail inside the lysosome. Thus, these results lend credence to the idea that toxin enters the cytoplasm from the lysosomal compartment.

Additional Information

© 1981 by the National Academy of Sciences. Communicated by Warren L. Butler, September 30, 1980. Support for this work was provided through a training grant from the U.S. Public Health Services (GM07169-05 to J.J.D.) and research grants from the National Science Foundation (PCM7726862 to M.I.S.), the National Institutes of Health (EY-02084 to M.M.), and the Office of Naval Research (N00014-79-C-0748 to M.M. and M.I.S.). The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.


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