SUMMARY: Diverse enzyme changes were obtained in grown at deficient, optimal and toxic levels of Mo, Cu and Fe. These included mutual antagonisms between the metals, single effects of one element or additive ones of more than one element. Cytochrome oxidase content, enhanced by Cu treatment, was decreased by increasing Mo; the reverse relationship was obtained with nitrate reductase. Cytochrome and nitrite reductases, however, were depressed by amounts both of Cu and Mo which were toxic to growth; the effects were additive. Single effects were as follows: TPNH diaphorase and acid phosphatase were depressed by Cu and Mo excess respectively; the iron enzymes and the two diaphorases were more active when Fe was increased from deficiency to sufficiency level. High iron concentrations increased nitrate reductase but depressed the nitrite system. Molybdenum is shown to inhibit acid phosphatase competitively , presumably by forming a molybdo-phosphate addition compound with the substrate. Cu dispersed this complex and restored the enzyme activity to normal. Vanadate or tungstate had a similar effect to molybdate in depressing the enzyme but Cu was found to reverse the inhibition.

Thus it appears that antagonisms between metals in nutrition experiments may be related to their effects on certain enzymes as illustrated here for Cu, Mo and Fe in


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