Comparison of Assays for the Quantitation of Superoxide Dismustase in Apple and Potato Tissues

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  • 1 USDA, Agricultural Research Service, National Center for Agricultural Utilization Research, Peoria, IL 61604.

The enzyme superoxide dismutase (SOD; EC catalyzes the conversion of the superoxide radical (\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{O}_{2}^{-}\) \end{document}) to O2 and H2O2. SOD is thought to be critical in delaying aging and senescence in plant tissues such as apple fruit and potato tubers. A variety of assays have been reported for the quantitation of SOD based on the inhibition of O2-driven reactions. Four assays were examined, including 1) the reduction of nitro blue tetrazolium (NBT) by \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{O}_{2}^{-}\) \end{document}generated by the reaction of cysteine and FeCl3; 2) the reduction of NBT by \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{O}_{2}^{-}\) \end{document}generated by photochemical activation of riboflavin; 3) the inhibition of nitrite formation from hydroxylammonium chloride (nitrite subsequently converts sulfanilic acid to a diazonium compound, which reacts with α-naphthylamine to form a red azo compound); and 4) the autoxidation of hematoxylin to hematein by \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{O}_{2}^{-}\) \end{document}. In all cases, the production of colored compounds was inversely proportional to SOD activity. Although all of the assays were successful in quantitating SOD activity, assays 1 and 4 appeared simplest to use and had the fewest drawbacks.

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