A Note on the Ammonium Sulphate Precipitation of the Active Principle of the Culture Filtrates of C. diphtheriae

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Abstract
The authors find that the active principle giving specific flocculation with diphtheria antitoxin can be entirely salted out of culture filtrates of Corynebacterium diphtheriae by complete saturation with (NH4)2SO4, provided the filtrates are untreated with any chemical agent and are adjusted to [rho][ETA] 8 before precipitation. Certain chemical agents (e.g., phenol or acid) interfere with complete recovery of the active principle by (NH4)2SO4 precipitation. Complete precipitation is never obtained by use of acid; the maximum recovery never exceeded 39% of the active principle. By salting out, the purest pre-cipitate is recovered at 2/3 saturation (NH4)2SO4. The acid precipitate produced at the isoelectric point, however, is purer, relative to the original filtrate, than that obtained by use of (NH4)2SO4 at any concentra-tion. The determination of purity is based on the LF units per mg. of N of the original culture filtrate.

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