title: Interactions between diphtheria toxin entry and anion transport in Vero cells. II. Inhibition of anion antiport by diphtheria toxin.
abstract: 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.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D027321:Anion Transport Proteins; D000838:Anions / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002460:Cell Line; D002712:Chlorides / Q000378:metabolism; D002522:Chlorocebus aethiops; D006224:Cricetinae; D004167:Diphtheria Toxin / Q000378:metabolism / Q000494:pharmacology*; D006367:HeLa Cells / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007668:Kidney; D007700:Kinetics; D007739:L Cells / Q000378:metabolism; D008647:Mesocricetus; D051379:Mice; D014176:Protein Biosynthesis / Q000187:drug effects; D013431:Sulfates / Q000378:metabolism; D013861:Thiocyanates / Q000378:metabolism
chemical_list: D027321:Anion Transport Proteins; D000838:Anions; D002352:Carrier Proteins; D002712:Chlorides; D004167:Diphtheria Toxin; D013431:Sulfates; D013861:Thiocyanates; D000255:Adenosine Triphosphate; D002118:Calcium