Glutathione peroxidase from bovine lens: a selenoenzyme

Glutathione peroxidase was purified 12 000-fold to homogeneity from the bovine lens. Purification utilized ammonium sulfate, acetic acid and zinc sulfate precipitations, and covalent chromatography on activated Thiolsepharose 4B. The specific activity of the purified enzyme is 1600 and its estimated molecular weight is 140 000. It is a selenoenzyme, containing 4 mol of selenium per mol of enzyme. Its pH maximum is 7·9. The apparent K m s for glutathione, tert-butylhydroperoxide, cumene hydroperoxide and H 2O 2 are 2·9, 0·54, 0·65 and 0·045 m m, respectively. Iodoacetic acid irreversibly inhibits both the reduced and oxidized forms of the enzyme, whereas p-chloromercuriphenyl sulfonic acid only inhibits the oxidized form and N-ethyl maleimide, the reduced form.