Characterization of a soluble oxidoreductase from the thermophilic bacterium Carboxydothermus ferrireducens

An NAD(P)H-dependent oxidoreductase has been purified approximately 40-fold from the soluble protein fraction of the dissimilatory iron-reducing, anaerobic, thermophilic bacterium Carboxydothermus ferrireducens. The enzyme, a flavoprotein, has broad-substrate specificity-reducing Fe3+, Cr6+, and AQDS with rates of 0.31, 0.33, and 3.3 U mg(-1) protein and calculated NADH oxidation turnover numbers of 0.25, 0.25, and 2.5 s(-1), respectively. Numerous quinones are reduced via a two-electron transfer from NAD(P)H to quinone, thus participating in managing oxidative stress by avoiding the formation of semiquinone radicals.