Superoxide anion radical accumulation

The loss of cytochrome c partly blocks electron flow between complex in and complex IV of the mitochondrial respiratory chain, thus causing the accumulation of electrons within complex I and complex IE. The accumulated electrons react with oxygen to form the superoxide anion radical and other ROS, triggering the... 

The production of superoxide anions is one of the major factors involved in NO toxicity because superoxide anions can react with NO to form the highly toxic free-radical peroxynitrite. A pivotal role for superoxide anions in NO-related insults is emphasized by results showing that transgenic mice overexpressing superoxide dismutase (SOD) are resistant to brain ischemia. Superoxide can protect against SNP-induced toxicity. Thus, the superoxide-scavenging properties of EGb 761 are likely to explain, at least in part, its ability to block cell death and the increase in reactive oxygen species accumulation induced by the two NO donors used here, SNP and SIN-1. 

The lung also possesses nonenzymatic antioxidants such as vitamin E, beta-carotene, vitamin C, and uric acid. Vitamin E is lipid-soluble and partitions into lipid membranes, where it is positioned optimally for maximal antioxidant effectiveness. Vitamin E converts superoxide anion, hydroxyl radical, and lipid peroxyl radicals to less reactive oxygen metabolites. Beta-carotene also accumulates in cell membranes and is a metabolic precursor to vitamin A. Furthermore, it can scavenge superoxide anion and react directly with peroxyl-free radicals, thereby serving as an additional lipid-soluble antioxidant. Vitamin C is widely available in both extracellular and intracellular spaces where it can participate in redox reactions. Vitamin C can directly scavenge superoxide and hydroxyl radical. Uric acid formed by the catabolism of purines also has antioxidant properties and primarily scavenges hydroxyl radical and peroxyl radicals from lipid peroxidation. 

The uptake of aminoglycosides into proximal renal tubular epithelial cells is limited to the luminal cell border and is saturable. Less frequent administration of doses larger than needed for saturation of this uptake may therefore reduce drug accumulation in the renal cortex (98). In vitro and in vivo data have provided evidence that partially reduced oxygen metabolites (superoxide anion, hydrogen peroxide, and hydroxyl radical), which are generated by renal cortical mitochondria, are important mediators of aminoglycoside-induced acute renal insufficiency (99). 

The herbicidal effect of paraquat is attributable to the formation of superoxide anion (02 ). Superoxide anion is very toxic compound and is formed by the reaction of oxygen with paraquat radical (paraquat ). Plants, algae, and cyanobacteria have ferredoxin-NADP reductase to form NADPH for the reduction of carbon dioxide (see below). The chemolithoautotrophs also have NAD(P) (NAD and NADP) reductase to form NAD(P)H for the reduction of carbon dioxide. Paraquat [mid-point redox potential at pH 7.0 (Emj 0) = -0.43 V] radical is produced when paraquat is reduced by the catalysis of ferredoxin-NAD(P) reductase or NAD(P) reductase, which catalyzes the reduction of many compounds with of around -0.4 V. Although the aerobic organisms (and even many anaerobic organisms) have superoxide dismutase (SOD) which detoxifies superoxide anion in cooperation with catalase [ascorbate peroxidase in the case of plants (Asada, 1999)], the anion accumulates in the organisms when it is over-produced beyond the capacity of SOD. 

Our knowledge of the structural properties and enzymic function of a large number of copper proteins has accumulated during the last few decades. The main results have been comprehensively reviewed 1—4) or presented at symposia (5—54). This survey is devoted to erythro-cuprein, one of the most actively studied copper proteins. Erythrocu-prein is sometimes called haemocuprein, hepatocuprein, cerebrocuprein, cytocuprein, or erythro-cupro-zinc protein. Alternatively, the name superoxide dismutase has been suggested as descriptive of its activity the enzyme-catalyzed disproportionation of anionic monovalent superoxide radicals. However, whether or not the enzymic reaction is specific for Oi- still needs to be investigated1). Thus, the name erythrocuprein is used throughout this review. 

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