This paper, authored by L. Flohé, W.A. GüNZLER, and H.H. SchOCK, investigates the presence of selenium in glutathione peroxidase (GSH peroxidase) from bovine blood. Selenium was previously discovered as an essential trace element for mammals, and its role in antioxidant mechanisms was hypothesized to be related to GSH-dependent metabolism of hydroperoxides. The authors used neutron activation analysis to determine the selenium content of GSH peroxidase, finding four grams of selenium per mole of enzyme, suggesting one atom of selenium per subunit. This finding supports the hypothesis that selenium is an essential component of GSH peroxidase. The study also highlights the potential significance of selenium in explaining the pathological symptoms of selenium deficiency, particularly those related to lipid peroxidation in biological membranes. The research was supported by the Deutsche Forschungsgemeinschaft and the Bundesministerium für Bildung und Wissenschaft of the German Federal Republic.This paper, authored by L. Flohé, W.A. GüNZLER, and H.H. SchOCK, investigates the presence of selenium in glutathione peroxidase (GSH peroxidase) from bovine blood. Selenium was previously discovered as an essential trace element for mammals, and its role in antioxidant mechanisms was hypothesized to be related to GSH-dependent metabolism of hydroperoxides. The authors used neutron activation analysis to determine the selenium content of GSH peroxidase, finding four grams of selenium per mole of enzyme, suggesting one atom of selenium per subunit. This finding supports the hypothesis that selenium is an essential component of GSH peroxidase. The study also highlights the potential significance of selenium in explaining the pathological symptoms of selenium deficiency, particularly those related to lipid peroxidation in biological membranes. The research was supported by the Deutsche Forschungsgemeinschaft and the Bundesministerium für Bildung und Wissenschaft of the German Federal Republic.