PMID: 7085634Jul 10, 1982Paper

Entry of the toxic proteins abrin, modeccin, ricin, and diphtheria toxin into cells. II. Effect of pH, metabolic inhibitors, and ionophores and evidence for toxin penetration from endocytotic vesicles.

The Journal of Biological Chemistry
K Sandvig, S Olsnes


The toxicity of abrin, modeccin, and ricin to Vero cells was maximal at neutral and slightly alkaline pH, and it was strongly reduced at pH 6.0 and below. Diphtheria toxin was most toxic at low pH. Binding and endocytosis of abrin, modeccin, and ricin did not vary much within the pH range tested. High concentrations of the carboxylic ionophore Br-X-537A, protected against all four toxins. Combined treatment of cells with an inhibitor of glycolysis and an uncoupler of oxidative phosphorylation strongly inhibited endocytosis of toxins and protected against intoxication. The protective effect of Ca2+ deprivation, of pH 6.0, and of metabolic inhibitors disappeared soon after transfer of the cells to normal medium, whereas the protective effect of Br-X-537A and of trifluoperazine disappeared slowly. The decay rate of the protection by NH4Cl and by the ionophore A23187 differed with the different toxins. Cells exposed to abrin, modeccin, and ricin under protective conditions which did not inhibit endocytosis of the toxins (Ca2+ deprivation, pH 6.0, Br-X-537A), and then treated with antitoxins to inactivate extracellular toxin, were intoxicated when the protection was released. In contrast, cells exposed to toxins while endocytosis wa...Continue Reading

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