Enhancing Effect of Nucleic Acids and Their Derivatives in the Reduction of Cytochrome c by Ferrous Ions

Additional properties of the Ferrobacillus ferrooxidans heatstable iron-cytochrome c "reductase," in view of the doubts of its protein or enzymatic nature, were studied and compared with those of various nucleic acids and their derivatives in enhancing the reduction of cytochrome c by ferrous ions with the following results.Calf thymus deoxyribonucleic acid, salmon sperm DNA, yeast RNA, and the derivatives, RNA core and apurinic acid, enhance the reduction of cytochrome c by ferrous ions at physiological pH values (pH 5.7 to 6.0).The action of these compounds is inhibited by atebrin, reduced glutathione, p-hydroxymercuribenzoate, and cysteine, and also by several metal ions including Fe+++, Co++, Ni++, Cu++, and Zn++.The products of the reaction, namely reduced cytochrome c and ferric ions, inhibited 60 and 100% at concentrations of 8 X 10e5 M and 10m3 M, respectively.Ah of the above nucleic acids and derivatives showed substrate saturation curves for both reactants with K,,, values ranging from 10F4 M to 7.5 X low4 M forFeS04-7H20 and from 1.8 X low6 M to 8 X low5 M for oxidized cytochrome c.III all of the above respects their properties resembled closely those displayed by the heat-stable iron-cytochrome c "reductase" from F. ferrooxidans.The prolonged action of DNase on calf thymus DNA and on the heat-stable iron-cytochrome c 'reductase" preparation from F. ferrooxidans rendered iron-cytochrome c reducing activity dialyzable but did not destroy it.RNAase had no effect on the F. ferrooxidans preparation but rendered the iron-cytochrome c reductase activity of yeast RNA dialyzable.This evidence indicates that DNA is associated with the heat-stable preparation from F. ferrooxidans.The action of DNAase on serum bovine albumin produced no dialyzable protein, suggesting that no protease is present in the DNAase that could account for its effect.The proteolytic enzyme Pronase partially inhibited the enhancement of cytochrome c reduction by iron with calf thymus DNA and the heat-stable preparation from F. ferro- oxidans, an inhibition that could be reversed by heating in a