Dithiothreitol generates an activated 250,000 mol. wt form of Clostridium difficile toxin B

The potent cytotoxin of Clostridium difficile, toxin B, is internalized by endocytosis and activated intracellularly by an unidentified mechanism. Here it is shown that dithiothreitol treatment of toxin B resulted in (1) a mol. wt of 250,000 which is the smallest species of this toxin shown to be cytotoxic; (2) an increased endpoint titre; and (3) translocation of plasma membrane-bound toxin across the membrane at pH 4.5. Treatment with dithiothreitol can thus mimic intracellular activation of the toxin. Radiolabelling of highly purified toxin with retained activity, as well as the 32 N-terminal amino acids and the amino acid composition, is also presented.