Catalases Are NAD(P)H-Dependent Tellurite Reductases

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 (TeO(3) (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

A genetic analysis of in vivo selenate reduction by Salmonella enterica serovar Typhimurium LT2 and Escherichia coli K12

The twin-arginine transport (Tat) system is dedicated to the translocation of folded proteins across the bacterial cytoplasmic membrane. Proteins are targeted to the Tat system by signal peptides containing a twin-arginine motif. In Salmonella enterica serovar Typhimurium and Escherichia coli many Tat substrates are known or predicted to bind a molybdenum cofactor in the cytoplasm prior to export. In the case of N- and S-oxide reductases, co-ordination of molybdenum cofactor insertion with protein export involves a 'Tat proofreading' process where chaperones of the TorD family bind the signal peptides, thus preventing premature export. Here, a genetic approach was taken to determine factors required for selenate reductase activity in Salmonella and E. coli. It is reported for both biological systems that an active Tat translocase and a TorD-like chaperone (DmsD) are required for complete in vivo reduction of selenate to elemental red selenium. Further mutagenesis and in vitro biophysical experiments implicate the Salmonella ynfE gene product, and the E. coli YnfE and YnfF proteins, as putative Tat-targeted selenate reductases

Associations between toxic metals in follicular fluid and in vitro fertilization (IVF) outcomes

PURPOSE: We previously reported associations between trace concentrations of Hg, Cd and Pb in blood and urine and reproductive outcomes for women undergoing in-vitro fertilization (IVF). Here we assess measurements in single follicular fluid (FF) specimens from 46 women as a presumably more relevant marker of dose for reproductive toxicity. METHODS: FF specimens were analyzed for Hg, Cd and Pb using sector field-inductively coupled plasma-mass spectrometry (SF-ICP-MS). Variability sources were assessed by nested ANOVA. Multivariable regression was used to evaluate associations for square root transformed metals with IVF outcomes, adjusting for confounders. RESULTS: An inverse association is detected for FF Pb and fertilization (relative risk (RR) = 0.68, P = 0.026), although positive for Cd (RR = 9.05, P = 0.025). While no other statistically significant associations are detected, odds ratios (OR) are increased for embryo cleavage with Hg (OR = 3.83, P = 0.264) and Cd (OR = 3.18, P = 0.644), and for embryo fragmentation with Cd (OR = 4.08, P = 0.586) and Pb (OR = 2.22, P = 0.220). Positive estimates are observed for Cd with biochemical (RR = 19.02, P = 0.286) and clinical pregnancies (RR = 38.80, P = 0.212), yet with very low precision. CONCLUSIONS: We have identified associations between trace amounts of Pb and Cd in FF from a single follicle, and oocyte fertilization. Yet, the likelihood of biological variation in trace element concentrations within and between follicles, coupled with levels that are near the limits of detection suggest that future work should examine multiple follicles using a ‘one follicle-one oocyte/embryo’ approach. A larger study is merited to assess more definitively the role that these environmental factors could play with respect to egg quality in IVF programs