On page 5817 in the 2 June 2011 issue, there is an error in Figure 1: the Fenton chemistry cycle is drawn with the arrows in the opposing direction to the true nature of the cycle. The corrected Figure 1 is shown.
Physiologic ROS homeostasis networks. Univalent reduction of oxygen results in the formation of superoxide (O2•−), which can occur as a result of NADPH oxidase (NOX) activity, and also as a by-product of oxidative phosphorylation, primarily at complex I in the mitochondrial electron transport chain (ETC). Superoxide may act as a reductant or an oxidant and is a key molecule in several subsequent physiologic reactions. Most of the superoxide generated in vivo is converted into hydrogen peroxide (H2O2) primarily by the actions of superoxide dismutases, which exist in cytosolic (SOD1), mitochondrial (SOD2), and extracellular (SOD3) isoforms. H2O2 levels are tightly regulated by several mechanisms, including the actions of catalase, the glutathione peroxidase (GPX) system, and peroxiredoxins (Prx). H2O2 may be further processed by the actions of myeloperoxidase (MPO) during an immune response to form hypochlorous acid (HOCl), which may in turn react with superoxide to form hydroxyl radicals. Hydroxyl radicals may also be formed from H2O2 by Fenton chemistry, which may occur in the presence of free metal cations such as Fe2+ or Cu+. Where superoxide production and production of nitric oxide (NO•) are colocalized, reactive nitrogen species (RNS) may be formed, with the proximal species being peroxynitrite. Various RNS may then form via further chemical reactions with other ROS or RNS. This network of ROS and RNS production can be disrupted or biased in the presence of various compounds such as diphenyleneiodonium (DPI), which inhibits flavoproteins including the NOX oxidase family, ion chelators that can terminate Fenton chemistry cycles, and l-arginine analogs such as l-monomethyl arginine (L-NMMA), which inhibits nitric oxide synthase. Green represents molecular oxygen, blue are ROS derived from O2, and red represents nitric oxide and other RNS.
Physiologic ROS homeostasis networks. Univalent reduction of oxygen results in the formation of superoxide (O2•−), which can occur as a result of NADPH oxidase (NOX) activity, and also as a by-product of oxidative phosphorylation, primarily at complex I in the mitochondrial electron transport chain (ETC). Superoxide may act as a reductant or an oxidant and is a key molecule in several subsequent physiologic reactions. Most of the superoxide generated in vivo is converted into hydrogen peroxide (H2O2) primarily by the actions of superoxide dismutases, which exist in cytosolic (SOD1), mitochondrial (SOD2), and extracellular (SOD3) isoforms. H2O2 levels are tightly regulated by several mechanisms, including the actions of catalase, the glutathione peroxidase (GPX) system, and peroxiredoxins (Prx). H2O2 may be further processed by the actions of myeloperoxidase (MPO) during an immune response to form hypochlorous acid (HOCl), which may in turn react with superoxide to form hydroxyl radicals. Hydroxyl radicals may also be formed from H2O2 by Fenton chemistry, which may occur in the presence of free metal cations such as Fe2+ or Cu+. Where superoxide production and production of nitric oxide (NO•) are colocalized, reactive nitrogen species (RNS) may be formed, with the proximal species being peroxynitrite. Various RNS may then form via further chemical reactions with other ROS or RNS. This network of ROS and RNS production can be disrupted or biased in the presence of various compounds such as diphenyleneiodonium (DPI), which inhibits flavoproteins including the NOX oxidase family, ion chelators that can terminate Fenton chemistry cycles, and l-arginine analogs such as l-monomethyl arginine (L-NMMA), which inhibits nitric oxide synthase. Green represents molecular oxygen, blue are ROS derived from O2, and red represents nitric oxide and other RNS.
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