The enzyme-linked immunosorbent assay and the Chinese hamster ovary floating cell assay for cholera toxin have proven to be sensitive and reliable tests for determining the antigenic and biological characteristics of Salmonella toxin, respectively. The addition of mitomycin C to the culture media 3 h after inoculation resulted in increased amounts of Salmonella toxin in culture filtrates but had the reverse effect on cell sonic extracts. Our data suggested that the increased amounts of Salmonella toxin culture filtrates caused by mitomycin C were due to cell lysis, resulting in the release of intracellular toxin, rather than to an increase in the synthesis of Salmonella toxin. The biological activity of Salmonella toxin was heat labile at 100 degrees C. The antigenic structure of the toxin appeared to remain intact after exposure to temperatures as high as 100 degrees C but was altered somewhat when the toxin was subjected to autoclaving. The toxin had an isoelectric point in the pH range from 4.3 to 4.8 and an estimated molecular weight which appeared to be more than 110,000. With the exception of the range for its isoelectric point, its molecular weight, and its low concentration in filtrates and sonic extracts, Salmonella toxin was very similar in biological and antigenic characteristics to cholera toxin. The antigenic and biological assays described here provide an effective basis for extending our study of Salmonella toxin.
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