SUMMARY: The reaction between staphylococcal α-toxin and a toxin-inactivating substance (TIS) excreted by was found to proceed optimally at about pH 7·8, and in the temperature range 36–44°. A modified assay method, based on these findings, was used to follow TIS excretion by the mould. Appearance of the active principle in the culture filtrate followed closely upon the period of active sugar utilization by the mould. TIS was excreted in quiescent cultures, but not in shake cultures. The presence of certain nutritional factors found in beef heart infusion appeared to be necessary for TIS excretion, since detoxifying activity could not be detected in filtrates from cultures of the mould grown in the absence of this nitrogen source. The marked correlation between detoxifying and protease activities of culture filtrates during growth of the mould under various conditions, as well as during purification of TIS, and its inactivation by heat and by DFP, suggested that both activities were manifestations of the same enzymic reaction.


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