Superoxide dismutase, reaction

Superoxide is formed (reaction 1) in the red blood cell by the auto-oxidation of hemoglobin to methemo-globin (approximately 3% of hemoglobin in human red blood cells has been calculated to auto-oxidize per day) in other tissues, it is formed by the action of enzymes such as cytochrome P450 reductase and xanthine oxidase. When stimulated by contact with bacteria, neutrophils exhibit a respiratory burst (see below) and produce superoxide in a reaction catalyzed by NADPH oxidase (reaction 2). Superoxide spontaneously dismu-tates to form H2O2 and O2 however, the rate of this same reaction is speeded up tremendously by the action of the enzyme superoxide dismutase (reaction 3). Hydrogen peroxide is subject to a number of fates. The enzyme catalase, present in many types of cells, converts... 

Time-course of human manganese superoxide dismutase reaction after generation of superoxide by pulse radiolysisT The experiment demonstrates decrease in absorbance at 250 nm (e = 2000 M cm ) for a solution containing 0.5/aM enzyme, 50/aM EDTA, 10 mM sodium formate, and 2 mM sodium pyrophosphate at pH 9.4 and 20°C. The starting concentrations of superoxide were 11.6 /xhA (upper curve), 6.5 /aM (middle curve), and 3.4 /aM (lower curve). The calculated progress curves shown as solid lines were obtained by using the KINSIM software and the model of Bull et aF Reproduced here with the permission of the authors and the American Chemical Society. 

R6. Rotilio, G., Morpurgo, L., Calabrese, L., and Mondovi, B On the mechanism of superoxide dismutase reaction of the bovine enzyme with hydrogen peroxide and ferrocyanide. Biochim. Biophys. Acta 302, 229-235 (1973). 

When H2O2 is a necessary component of a luminescence system, it can be removed by catalase. If a luminescence system involves superoxide anion, the light emission can be quenched by destroying O2 with superoxide dismutase (SOD). The ATP cofactor usually present in the fresh extracts of the fireflies and the millipede Luminodesmus can be used up by their spontaneous luminescence reactions, eventually resulting in dark (nonluminous) extracts containing a luciferase or photoprotein. The process is, however, accompanied by a corresponding loss in the amount of luciferin or photoprotein. The use of ATPase and the elimination of Mg2+ in the extract may prevent such a loss. 

Suzuki, N., etal. (1991). Reaction rates for the chemiluminescence of Cypridina luciferin analogs with superoxide a quenching experiment with superoxide dismutase. Agric. Biol. Chem. 55 157-160. 

As described in Section 15.7, enzymes are the catalysts of biological reactions. Without enzymes, most of the reactions that occur in a cell would be imperceptibly slow. Cations of transition metals play essential roles in the mechanisms of many enzyme-catalyzed reactions. Here we introduce just one representative example, superoxide dismutase. 

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. 

Carloni et al.91 applied the DFT(PZ) calculations to investigate the electronic structure of various models of oxydized and reduced Cu, Zn superoxide dismutase. The first stage of the enzymatic reaction involves the electron transfer from Cu" ion to superoxide. The theoretical investigations provided a detailed description of the electronic structure of the molecules involved in the electron transfer process. The effect of charged groups, present in the active center, on the electron transfer process were analyzed and the Argl41 residue was shown to play a crucial role. 

Protection from unwanted side products of oxygen reactions uses the cytoplasmic Cu/Zn superoxide dismutase and vesicular haem catalases as in all eukaryotes as... 

J.M. McCord and I. Fridovich, Utility of superoxide dismutase in studying free radical reactions. II. Mechanism of the mediation of cytochrome c reduction by a variety of electron carriers. J. Biol. Chem. 245,1374-1377 (1970). 

D. Cocco, L. Calabrese, A. Rigo, F. Marmocchi, and G. Rotitlio, Preparation of selectively metal-free and metal-substituted derivatives by reaction of Cu-Zn superoxide dismutase with diethyldithiocar-bamate. Biochem. J. 199, 675-680 (1981). 

Several enzymes have been immobilized in sol-gel matrices effectively and employed in diverse applications. Urease, catalase, and adenylic acid deaminase were first encapsulated in sol-gel matrices [72], The encapsulated urease and catalase retained partial activity but adenylic acid deaminase completely lost its activity. After three decades considerable attention has been paid again towards the bioencapsulation using sol-gel glasses. Braun et al. [73] successfully encapsulated alkaline phosphatase in silica gel, which retained its activity up to 2 months (30% of initial) with improved thermal stability. Further Shtelzer et al. [58] sequestered trypsin within a binary sol-gel-derived composite using TEOS and PEG. Ellerby et al. [74] entrapped other proteins such as cytochrome c and Mb in TEOS sol-gel. Later several proteins such as Mb [8], hemoglobin (Hb) [56], cyt c [55, 75], bacteriorhodopsin (bR) [76], lactate oxidase [77], alkaline phosphatase (AP) [78], GOD [51], HRP [79], urease [80], superoxide dismutase [8], tyrosinase [81], acetylcholinesterase [82], etc. have been immobilized into different sol-gel matrices. Hitherto some reports have described the various aspects of sol-gel entrapped biomolecules such as conformation [50, 60], dynamics [12, 83], accessibility [46], reaction kinetics [50, 54], activity [7, 84], and stability [1, 80],... 

Adults require 1-2 mg of copper per day, and eliminate excess copper in bile and feces. Most plasma copper is present in ceruloplasmin. In Wilson s disease, the diminished availability of ceruloplasmin interferes with the function of enzymes that rely on ceruloplasmin as a copper donor (e.g. cytochrome oxidase, tyrosinase and superoxide dismutase). In addition, loss of copper-binding capacity in the serum leads to copper deposition in liver, brain and other organs, resulting in tissue damage. The mechanisms of toxicity are not fully understood, but may involve the formation of hydroxyl radicals via the Fenton reaction, which, in turn initiates a cascade of cellular cytotoxic events, including mitochondrial dysfunction, lipid peroxidation, disruption of calcium ion homeostasis, and cell death. 

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