Catalases Are NAD(P)H-Dependent Tellurite Reductases

Abstract

Reactive oxygen species damage intracellular targets and are implicated in cancer, genetic disease, mutagenesis, and aging. Catalases are among the key enzymatic defenses against one of the most physiologically abundant reactive oxygen species, hydrogen peroxide. The well-studied, heme-dependent catalases accelerate the rate of the dismutation of peroxide to molecular oxygen and water with near kinetic perfection. Many catalases also bind the cofactors NADPH and NADH tenaciously, but, surprisingly, NAD(P)H is not required for their dismutase activity. Although NAD(P)H protects bovine catalase against oxidative damage by its peroxide substrate, the catalytic role of the nicotinamide cofactor in the function of this enzyme has remained a biochemical mystery to date. Anions formed by heavy metal oxides are among the most highly reactive, natural oxidizing agents. Here, we show that a natural isolate of Staphylococcus epidermidis resistant to tellurite detoxifies this anion thanks to a novel activity of its catalase, and that a subset of both bacterial and mammalian catalases carry out the NAD(P)H-dependent reduction of soluble tellurite ion (TeO3 2−) to the less toxic, insoluble metal, tellurium (Te°), in vitro. An Escherichia coli mutant defective in the KatG catalase/peroxidase is sensitive to tellurite, and expression of the S. epidermidis catalase gene in a heterologous E. coli host confers increased resistance to tellurite as well as to hydrogen peroxide in vivo, arguing that S. epidermidis catalase provides a physiological line of defense against both of these strong oxidizing agents. Kinetic studies reveal that bovine catalase reduces tellurite with a low Michaelis-Menten constant, a result suggesting that tellurite is among the natural substrates of this enzyme. The reduction of tellurite by bovine catalase occurs at the expense of producing the highly reactive superoxide radical.

Bacterial Toxicity of Potassium Tellurite: Unveiling an Ancient Enigma

“…Superoxide generation was evaluated using an in vitro tellurite reduction assay previously developed in our laboratory [34]. The system makes use of the O 2 − specific reactive compound WST-1.…”

“…These results also favor the idea that tellurite does not produce peroxide inside E. coli as does the hydrogen peroxide-hypersensitive katG strain which showed a negligible increase in sensitivity to K 2 TeO 3 (Table 2). E. coli cells over expressing a Staphylococcus epidermidis catalase gene showed a slight increase in tellurite resistance suggesting that the role of H 2 O 2 in tellurite resistance, if any, is not an important feature of K 2 TeO 3 toxicity [34].…”

“…Superoxide radical specifically reduces 2-(4-Iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium (WST-1, Cell Technology Lab) to the soluble form WST-formazan that can be easily detected at 438 nm. We have previously established that tellurite can be reduced by different enzymes including catalase [4], [26], [34]. Reduction mix contained 200 µg/ml of purified bovine liver catalase, 1 mM NADPH, 1 mM potassium tellurite and 50 mM Tris-HCl buffer pH 7.0.…”

Escherichia coli YqhD Exhibits Aldehyde Reductase Activity and Protects from the Harmful Effect of Lipid Peroxidation-derived Aldehydes

“…We found that YqhD was highly induced when cells were grown in the presence of K 2 TeO 3 . This result and the fact that an important pathway of tellurite toxicity involves superoxide generation (4,27) prompted us to evaluate the role that YqhD could have in E. coli resistance to tellurite and other oxidative stress elicitors.…”

“…Although cells overexpressing yqhD showed increased tolerance to compounds whose toxicity involves superoxide generation like paraquat and potassium tellurite (4,27), the hydroxyl radical-generating chromate anion (5), and hydrogen peroxide, E. coli ⌬yqhD showed increased sensitivity to all these compounds (Table 2). To assess whether YqhD-mediated resistance phenotype was also related to cytoplasm thiol depletion (especially GSH), the effect of YqhD on E. coli resistance to oxidant compounds that involve thiol oxidation like diamide and cadmium chloride (28) was determined.…”