Isolation and characterization of the cytosolic and mitochondrial superoxide dismutases of maize

The cytosolic and mitochondrial forms of Superoxide dismutase have been purified to homogeneity from an inbred line of maize. The cytosolic isozymes SOD-2 and SOD-4 are dimers with a molecular weight of 31,000–33,000, composed of apparently equal subunits, and are remarkably similar with respect to their ultraviolet absorption spectra, antigenic specificity, and sensitivity to cyanide, azide, hydrogen peroxide, and diethyldithiocarbamate. These and other data suggest that both isozymes belong to the family of copper and zinc-containing Superoxide dismutases. The mitochondrial isozyme, SOD-3, is unlike the cytosolic isozymes in every parameter studied and appears to be similar to the mitochondrial manganese-containing Superoxide dismutases purified from other eukaryotic organisms. It is a tetramer with a molecular weight of approximately 90,000, composed of apparently equal subunits, and is insensitive to both 1 mm cyanide and hydrogen peroxide.