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Redox Equilibrium (redox + equilibrium)
Selected AbstractsOptical Spectra of Copper-Doped Zn-Phosphate GlassesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2007Adrian Goldstein Copper-containing, binary, Zn-phosphate glasses were melted under reductive conditions. The profile of their optical spectra and their color change drastically when the ZnO content of the host is modified. An increase in the host's ZnO concentration tilts the copper oxidation state's equilibria toward the reduced species Cu+ and Cu0. In hosts containing more than 52 mol% ZnO, the Cu0 aggregates precipitate upon melt cooling to form ruby glasses. The ruby color also appears in glasses including 50 mol% ZnO, after thermal treatments. The effect of ZnO increase, in the composition of binary Zn-phosphate glasses, on the redox equilibria of a copper dopant, is inverse to that caused by increase of Na2O content in the case of Na-phosphate hosts. [source] Kinetics of electron transfer from NADH to the Escherichia coli nitric oxide reductase flavorubredoxinFEBS JOURNAL, Issue 3 2007João B. Vicente Escherichia coli flavorubredoxin (FlRd) belongs to the family of flavodiiron proteins (FDPs), microbial enzymes that are expressed to scavenge nitric oxide (NO) under anaerobic conditions. To degrade NO, FlRd has to be reduced by NADH via the FAD-binding protein flavorubredoxin reductase, thus the kinetics of electron transfer along this pathway was investigated by stopped-flow absorption spectroscopy. We found that NADH, but not NADPH, quickly reduces the FlRd-reductase (k = 5.5 ± 2.2 × 106 m,1·s,1 at 5 °C), with a limiting rate of 255 ± 17 s,1. The reductase in turn quickly reduces the rubredoxin (Rd) center of FlRd, as assessed at 5 °C working with the native FlRd enzyme (k = 2.4 ± 0.1 × 106 m,1·s,1) and with its isolated Rd-domain (k , 1 × 107 m,1·s,1); in both cases the reaction was found to be dependent on pH and ionic strength. In FlRd the fast reduction of the Rd center occurs synchronously with the formation of flavin mononucleotide semiquinone. Our data provide evidence that (a) FlRd-reductase rapidly shuttles electrons between NADH and FlRd, a prerequisite for NO reduction in this detoxification pathway, and (b) the electron accepting site in FlRd, the Rd center, is in very fast redox equilibrium with the flavin mononucleotide. [source] Phototoxicity in Human Retinal Pigment Epithelial Cells Promoted by Hypericin, a Component of St. John's Wort,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2007Albert R. Wielgus ABSTRACT St. John's wort (SJW), an over-the-counter antidepressant, contains hypericin, which absorbs light in the UV and visible ranges. In vivo studies have determined that hypericin is phototoxic to skin and our previous in vitro studies with lens tissues have determined that it is potentially phototoxic to the human lens. To determine if hypericin might also be phototoxic to the human retina, we exposed human retinal pigment epithelial (hRPE) cells to 10,7 to 10,5 M hypericin. Fluorescence emission detected from the cells (,ex = 488 nm; ,em = 505 nm) confirmed hypericin uptake by human RPE. Neither hypericin exposure alone nor visible light exposure alone reduced cell viability. However when irradiated with 0.7 J cm,2 of visible light (, > 400 nm) there was loss of cell viability as measured by MTS and lactate dehydrogenase assays. The presence of hypericin in irradiated hRPE cells significantly changed the redox equilibrium of glutathione and a decrease in the activity of glutathione reductase. Increased lipid peroxidation as measured by the thiobarbituric acid reactive substances assay correlated to hypericin concentration in hRPE cells and visible light radiation. Thus, ingested SJW is potentially phototoxic to the retina and could contribute to retinal or early macular degeneration. [source] Hierarchical Mechanochemical Switches in AngiostatinCHEMBIOCHEM, Issue 11 2006Fabio Grandi Abstract We wish to propose a novel mechanism by which the triggering of a biochemical signal can be controlled by the hierarchical coupling between a protein redox equilibrium and an external mechanical force. We have characterized this mechanochemical mechanism in angiostatin, and we have evidence that it can switch the access to partially unfolded structures of this protein. We have identified a metastable intermediate that is specifically accessible under thioredoxin-rich reducing conditions, like those met by angiostatin on the surface of a tumor cell. The structure of the same intermediate accounts for the unexplained antiangiogenic activity of angiostatin. These findings demonstrate a new link between redox biology and mechanically regulated processes. [source] |