Crude and purified preparations of commercial alpha toxin from Clostridium peifringens were heated in physiological saline and in fractions separated from proteose peptone (Difco, 0120). Heating temperatures ranged from 55–95 C for 6–18 min. Alpha toxin remained active at temperatures ⩽ 85 C when heated in the presence of a fraction of proteose peptone having a MW ⩾ 50,000. At 95 C, some destruction was observed with a D-value of 444 min. In saline or a proteose peptone fraction having a MW < 50,000, heat inactivation of alpha toxin occurred at 65 C. Gel filtration revealed that heat protection was associated with complex formation of the alpha toxin with proteose peptone. Alpha toxin heat-treated in saline was reactivated when proteose peptone was added after heat treatment and the toxin was subsequently incubated in hemolysin indicator plates at 37 C for 24 h. Reactivation of alpha toxin was not observed when saline was added after the toxin was heat-treated and then incubated in hemolysin indicator plates at 37 C for up to 48 h.

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Author notes

1Journal Series Article 196-80 Ohio Agricultural Research and Development Center.

2Present Address: Department of Chemical Engineering, School of Engineering, University of Thessaloniki, Thessaloniki, Greece.