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Abstract
Several cations have been shown to affect protein and porphyrin formation by the G 12/6 strain of Corynebacterium diphtheriae. Cobaltous ion (Co++), at concentrations only slightly inhibiting growth, caused a marked inhibition of toxin formation. This effect was not produced by vitamin B12 or annulled by increases of cysteine or histidine concentration. Only a small proportion of added Co++, at concentrations above 0·2 μg./ml., was found in washed organisms, and the effect of Co++ was more marked than that of Fe++ when based on the weight of metal in the organisms. No appreciable proportion of the Co++ existed as a porphyrin complex. The growth inhibition caused by 5 μg. Co++/ml. was annulled by 0·6 μg. Fe++/ml. Co++ caused no increase in the cytochrome b content of the organism, nor did it affect the iron concentration required for maximum toxin formation. The combined toxin-inhibitory effect of Fe++ Co++ was considerably less than the sum of their independent effects. The bearing of these findings on the thesis that diphtheria toxin is the apoenzyme of cytochrome b is discussed.
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