Gene expression and development : the third of five volumes constituting the proceedings of the 4th International Congress on Isozymes, held in Austin, Texas, June 14-19, 1982 / editors, Mario C. Rattazzi, John G. Scandalios, Gregory S. Whitt.

International Congress on Isozymes

Date:: [cl983]

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Gene expression and development : the third of five volumes constituting the proceedings of the 4th International Congress on Isozymes, held in Austin, Texas, June 14-19, 1982 / editors, Mario C. Rattazzi, John G. Scandalios, Gregory S. Whitt. Source: Wellcome Collection.

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$18 / Scandalios AA AB BA BB AA AB BA BB Fig. 13. Superoxide dismutase from milky endoseфm assayed in the absence (control) and presence of 1 mM KCN. The mitochondrial isozyme, SOD-3, is resistant to KCN. AA and BB are the two phenotypes observed among maize inbred lines; AB and BA are hybrids between the two inbreds. SOD-1 is associated with the plastids; SOD-2, SOD-4, and SOD-5 are cytosolic isozymes (from Baum and Scandalios [1982]; with permission.) B. Intracellular Localization of Superoxide Dismutases Maize SOD has been resolved into four or five isozymes, depending on the inbred strain. These forms have been labeled SOD-1, SOD-2, SOD-3, SOD-4, and SOD-5, in order of their anodal migration (Fig. 13). Detailed genetic analysis using available SOD variants has shown that the SOD-1-4 isozymes are products of distinct nuclear gene loci [Baum and Scandalios, 1982]; detailed genetic analysis of SOD-5 is underway. It was further dem¬ onstrated that SOD-1, SOD-2, SOD-4, and SOD-5 are dimeric molecules and sensitive to cyanide, whereas SOD-3 is a tetrameric enzyme and is cyanide resistant (Fig. 13). All SOD isozymes have been purified and bio¬ chemically characterized [Baum and Scandalios, 1981]. Cell fractionation studies demonstrated that superoxide dismutase activity is associated with the cytosolic, mitochondrial, and chloroplastic fractions of maize seedlings. Sucrose gradient centrifugation has revealed the presence of the cyanide-resistant isozyme (SOD-3) in the mitochondria of maize scu- tella. Cyanide-sensitive SOD-1 is associated with chloroplasts and etioch- loroplasts prepared by differential centrifugation. Sucrose gradient centrif¬ ugation further confirmed the presence of superoxide dismutase in the intact chloroplast fraction of maize leaves [Baum and Scandalios, 1979]. Thus, it appears that SOD-1 is associated with intact chloroplasts and is not due to artifactual binding to membranes. SOD-2, SOD-4, and SOD-5 appear to be localized only in the cytosol.$