Oxygen superoxide

Potassium reacts with oxygen or air forming three oxides potassium monoxide, KaO potassium peroxide, KaOa and potassium superoxide, KOa. The nature of the product depends on oxygen supply. In limited supply of oxygen potassium monoxide is formed, while in excess oxygen, superoxide is... 

Because the erythrocyte is a relatively simplified cell with a circumscribed function it would seem that superoxide dismutase must act to prevent a deleterious effect of O2 on the erythrocyte s capacity to transport oxygen. Superoxide might react with hemoglobin to form a derivative which cannot reversibly bind O . One such reaction is to mediate the formation of methemoglobin, the derivative of hemoglobin in which the Fe in heme is converted to Fe . The ability of O to react with hemoglobin to form methemoglobin has been proposed to occur 201,207-209) jjj... 

Ilan, Y. A., G. Czapski, and D. Meisel, The one-electron transfer redox potential of free radicals 1. The oxygen/superoxide system , Biochim. Biophys. Acta, 430, 209-244 (1987). 

Oxygen Superoxide Hydrogen peroxide Hydroxyl radical Water... 

Figure 8. Oxygen, superoxide, and catalase reactions. SOD, superoxide dismutase CAT, catalase (24, 33)...

Copper in trace amounts can distort the kinetics of superoxide reactions with other compounds, because it effectively catalyses the dismutation reaction [143], Complexation by edta prevents this, as well as the reduction of hydrogen peroxide. Thus, edta protects the bases of DNA against copper-mediated damage [144]. However, edta will not protect if iron is involved, since rates of reaction between this metal complex and oxygen, superoxide or hydrogen peroxide are appreciable. 

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. 

Sawada, Y., lyanagi, T. and Yamazaki, I. (1975) Relation between redox potential and rate constants in reactions coupled with the system oxygen-superoxide. Biochemistry 14 3761-3764. 

However, if non-tertiary, oxyl radicals in aqueous solution are capable of undergoing a rapid 1,2-H-shift [44-46] [reaction (34)] in competition with fragmentation. Then after addition of oxygen, superoxide is eliminated [reaction (36)]. Thus under these conditions also, superoxide radicals are likely intermediates which are expected to react with peroxyl radiceds, reducing them to the corresponding hydroperoxides. These are abundant, though somewhat unstable, products in the radiolysis of air-saturated pyrimidine solutions. They are considered to be important precursors of the pyrimidine glycols observed under various conditions [1]. 

P.M. Wood, The redox potential of the system oxygen-superoxide, FEES Lett., 44 (1974)21. 

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