Superoxide Dismutase in Barley

Superoxide dismutese occurs in barley where it can be measured using a xanthine oxidase assay, but not using an assay based on the reduction of Nitro Blue Tetrazolium by photo-reduced riboflavin. Three isozymes are present in the grain: two are cyanide-sensitive and one, of lower activity, is not. Superoxide dismutase is mainly in the embryo of barley and develops in the acrospire, rootlets and endosperm during germination. Synthesis of this enzyme is accelerated by exogenous gibberellic acid. Significant quantities of superoxide dismutase survive kilning: lager malts contain ca 50% more than do ale malts. The enzyme is rapidly destroyed during mashing at 65°C, but large amounts survive mashing at 45°C.