SUMMARY A low-protein medium is described for the production of reasonable yields of ) -prototoxin. The -antigen in young cultures on this medium was virtually non-toxic, 99.8% being in the form of prototoxin. Its purity, estimated in terms of the protein content of crystalline -prototoxin, was 50%. Fractionation of concentrates of the antigen on columns of diethylaminoethyl- and carboxy-methyl-celluloses suggested that a number of proteins intermediate between -prototoxin and -toxin were present which differed from the latter in their isoelectric points in their activation ratios. The concentration and number of these intermediates increased as the incubation of cultures was prolonged. Since they could be fully converted to -toxin by trypsin it is probable that they were formed from -prototoxin by proteolytic or spontaneous degradation. In toxicity tests, death caused by unactivated antigen may be delayed. This evidence suggested that the intermediates were intrinsically non-toxic but could become activated in the animal body. The activation ratios might then be regarded as a measure of the ease with which the intermediates could be converted to toxin Physical data and the amino acid composition of crystalline -prototoxin are presented.


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