Isozymes of superoxide dismutase from wheat germ

Abstract

Wheat germ has been shown to contain three electrophoretically-distinct superoxide dismutases. One of these resembled the mangano-superoxide dismutases, which have been found in bacteria and in mitochondria 1–3, in that it was not inhibited by 0.2 mM cyanide but was inactivated by the Tsuchihashi 4 treatment with chloroform plus ethanol. The two remaining superoxide dismutases of wheat germ resembled the cupro-zinc enzymes, which have already been isolated from a wide range of eukaryotes 5–8, in being inhibited by cyanide but unaffected by treatment with chloroform plus ethanol. These two superoxide dismutases of wheat germ were isolated and characterized. Both were found to have a molecular weight of 31 000 and to be composed of two protomers of equal size which were joined by non-covalent interactions. Both contained 1 Cu 2+ and 1 Zn 2+ per protomer and exhibited similar catalytic properties. They did, however, exhibit distinct differences in amino acid composition chromatographic behavior on DE-32, optical and EPR spectra, stability towards sodium dodecyl sulfate and toward hydrogen peroxide and in electrophoretic mobility on polyacrylamide gels. Both of these enzymes were found in the seed heads of a commonly-grown non-hybrid strain of wheat (Cult. Var. Arthur); whereas the leaves and stalk of that strain contained only one of them. The reasons for the occurence of two isozymes of the cupro-zinc superoxide dismutase in wheat seeds remain unknown.