Purification of three fragments of the dermonecrotic toxin from Pasteurella multocida

Dermonecrotic toxin purified from sonicates of Pasteurella multocida was mildly trypsinized. The trypsinized preparations were reversibly dissociated into three polypeptides, with molecular weights of about 23,000 (fragment a), about 64,000 (fragment b), and about 74,000 (fragment c) by treatment with 100 mM dithiothreitol and 6 M urea. Upon removal of dithiothreitol and urea from the dissociated toxin by dialysis, the fragments reassociated and formed dermonecrotic toxin indistinguishable from the native toxin. The three fragments were separated from the dissociated toxin by gel filtration on a Sephadex G-200 column equilibrated with buffer containing 4 M urea and 1 mM dithiothreitol. The purified fragments a, b, and c did not show dermonecrotic activity for guinea pigs. Immunodiffusion and immunoelectrophoretic analysis with rabbit anti-dermonecrotic antiserum showed that the three purified fragments were antigenically distinct but had partial identity with the native toxin.