Oxygen superoxide dismutases

Superoxide dismutases are enzymes that catalyze the dismutation of superoxide radicals to hydrogen peroxide and molecular oxygen. Superoxide dismutases either have Cu and Zn (cytosolic isoform) or Mn " " (mitochondrial isoform). Reduction of hydrogen peroxides in cells is accomplished via catalases to water and oxygen. Cellular organelles called peroxisomes contain large quantities of catalase. In addition, NADPH quinone oxidoreductases (DT-diaphorase) also act as antioxidant enzymes by catalyzing two-electron reduction of quinones. 

Copper is one of the twenty-seven elements known to be essential to humans (69—72) (see Mineral nutrients). The daily recommended requirement for humans is 2.5—5.0 mg (73). Copper is probably second only to iron as an oxidation catalyst and oxygen carrier in humans (74). It is present in many proteins, such as hemocyanin [9013-32-3] galactose oxidase [9028-79-9] ceruloplasmin [9031 -37-2] dopamine -hydroxylase, monoamine oxidase [9001-66-5] superoxide dismutase [9054-89-17, and phenolase (75,76). Copper aids in photosynthesis and other oxidative processes in plants. 

Figure S.l The enzyme superoxide dismutase (SOD). SOD is a P structure comprising eight antiparallel P strands (a). In addition, SOD has two metal atoms, Cu and Zn (yellow circles), that participate in the catalytic action conversion of a superoxide radical to hydrogen peroxide and oxygen. The eight p strands are arranged around the surface of a barrel, which is viewed along the barrel axis in (b) and perpendicular to this axis in (c). [(a) Adapted from J.S. Richardson. The stmcture of SOD was determined in the laboratory of J.S. and D.R. Richardson, Duke University.)...

Superoxide is a free radical form of oxygen (02 ) that is damaging to cells. Superoxide is scavenged by the enzyme superoxide dismutase used by neutrophils to destroy microbes in the body. 

Propyl gallate is an antioxidant. It protects against oxidation by hydrogen peroxide and oxygen free radicals in a catalytic manner similar to superoxide dismutase. 

SUPEROXIDE DISMUTASE PROTECTS AEROBIC ORGANISMS AGAINST OXYGEN TOXICITY... 

Tissues are protected from oxygen toxicity caused by the superoxide free radical by the specific enzyme superoxide dismutase. 

Ito, Y., Hiraishi, H., Razandi, M., Terano, A., Harada, T. and Ivey, K.J. (1992). Role of cellular superoxide dismutase against reactive oxygen metabolite-induced cell dam e in cultured rat hepatocytes. Hepatology 16, 247-254. 

Niwa, Y., Soniya, K., Michelson, A.M. and Puget, K. (1985). Effect of liposomal-encapsulated superoxide dismutase on active oxygen-related disorders. A preliminary study. Free Rad. Res. Commun. 1, 137-153. 

Steer, M.L., Rutledge, P.L., Powers, R.E., Saluja, M. and Saluja, A.K. (1991). The role of oxygen-derived fiee radicals in two models of experimental acute pancreatitis effects of catalase, superoxide dismutase, dimethyl sulphoxide, and allopurinol. Klin. Wochenschr. 69, 1012-1017. 

Kensler, T.W. and Trush, M.A, (1983). Inhibition of oxygen radical metabolism in phorbol ester-activated polymorphonuclear leukocytes by an antitumor promoting copper complex with superoxide dismutase-mimetic activity. Biochem. Pharmacol. 32, 3485-3487. 

Lipid peroxidation (see Fig. 17.2) is a chain reaction that can be attacked in many ways. The chain reaction can be inhibited by use of radical scavengers (chain termination). Initiation of the chain reaction can be blocked by either inhibiting synthesis. of reactive oxygen species (ROS) or by use of antioxidant enzymes like superoxide dismutase (SOD), complexes of SOD and catalase. Finally, agents that chelate iron can remove free iron and thus reduce Flaber-Weiss-mediated iron/oxygen injury. 

The effectors of the mammalian host immune attack against filaria include reactive oxygen intermediates. Filarial nematodes express glutathione peroxidase, thioredoxin peroxidase and superoxide dismutase at their surface - enzymes believed to protect the nematode from this attack (Selkirk et al., 1998). A bacterial catalase gene has been identified that most probably derives from the endosymbiont genome (Henkle-Duhrsen et al., 1998) this enzyme may contribute with other enzymes to the protection of both Wolbachia and its nematode host from oxygen radicals. 

The mitochondrial dysfunctionality seen in manganese neurotoxicity might be related to the accumulation of reactive oxygen species (Verity, 1999). Mitochondrial Mn superoxide dismutase (MnSOD) is found to be low or absent in tumour cells and may act as a tumour suppressor. It is induced by inflammatory cytokines like TNF, presumably to protect host cells. In a rat model, iron-rich diets were found to decrease MnSOD activity, although a recent study reported that in rat epithelial cell cultures iron supplementation increased MnSOD protein levels and activity, but did not compromise the ability of inflammatory mediators like TNF to further increase the enzyme activity (Kuratko, 1999). 

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