The effect of the iron concentration in the medium on the concentration of toxin and coproporphyrin in the culture filtrate of a strain of has been found to differ quantitatively from that previously reported in the case of the P.W. 8 strain. Only 50-60% of the iron present in the medium, at all concentrations tested, was recoverable from the organisms. Of the total iron present in the medium, only 9% was found to be present in the organisms as a haem complex capable of measurement as its pyridine haemochromogen. On the basis of their iron contents protohaemin and iron coproporphyrin III are less active than ferrous sulphate in their effect on toxin yield. These findings do not support the hypothesis that diphtheria toxin is the protein moiety of the cytochrome of the cell.


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