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J. Biol. Chem., Vol. 261, Issue 4, 1553-1561, Feb, 1986
S Olsnes and K Sandvig
When cells with surface-bound diphtheria toxin were exposed to pH 4.5, the
toxin became shielded against lactoperoxidase-catalyzed radioiodination,
indicating that the toxin was inserted into the membrane. Cells thus
treated had strongly reduced ability to take up 36Cl-, 35SO4(2-), and
[14C]SCN-. The reduction of chloride uptake was strongest at neutral pH,
whereas that of sulfate was strongest at acidic pH. Lineweaver-Burk plots
indicated that the toxin treatment reduced the Jmax but not the Km for the
anions. The toxin also inhibited the NaCl-stimulated efflux of 35SO4(2-),
indicating that the toxin inhibits the antiporter. No inhibition was found
when toxin- treated cells were not exposed to low pH, whereas exposure to
pH 4.5 for 20 s induced close to maximal inhibition. Half-maximal
inhibition was obtained after exposure to pH 5.4. The concentration of
diphtheria toxin required to obtain maximal inhibition (0.3 micrograms/ml)
was sufficient to ensure close to maximal toxin binding to the cells. Even
in ATP-depleted cells and in the absence of permeant anions, low pH induced
inhibition of anion antiport in toxin-treated Vero cells. There was no
measurable inhibition of anion antiport in cells with little or no ability
to bind the toxin.
Interactions between diphtheria toxin entry and anion transport in Vero cells. II. Inhibition of anion antiport by diphtheria toxin
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