Three isozymes of superoxide dismutase were found in the soluble extract of kidney bean leaves. Two of them, purified to near homogeneous states, were inhibited by cyanide and by the antibody to spinach Cu, Zn-superoxide dismutase. Thus, both isozymes were the Cu and Zn containing enzyme that has a molecular weight of 32,000 and is composed of two subunits of equal size. Another isozyme was insensitive to cyanide and to the antibody, but was inactivated by acetone or heating. The cyanideinsensitive isozyme was not inactivated by H2O2showing that this isozyme is Mn-superoxide dismutase.
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