Abstract
Bovine erythrocyte glutathione (GSH) peroxidase (GPX, EC 1.11.1.9) was examined for GSH-dependent dehydroascorbate (DHA) reductase (EC 1.8.5.1) and thioltransferase (EC 1.8.4.1) activities. Using the direct assay method for GSH-dependent DHA reductase activity, GPX had akcat(app) of 140 ± 9 min−1and specificity constants (kcat/Km(app)) of 5.74 ± 0.78 × 102M−1s−1for DHA and 1.18 ± 0.17 × 103M−1s−1for GSH based on the monomer Mrof 22,612. Using the coupled assay method for thioltransferase activity, GPX had akcat(app) of 186 ± 9 min−1and specificity constants (app) of 1.49 ± 0.14 × 103M−1s−1for S-sulfocysteine and 1.51 ± 0.18 × 103M−1s−1for GSH based on the GPX monomer molecular weight. GPX has a higher specificity constant for S-sulfocysteine than DHA, and both assay systems gave nearly identical specificity constants for GSH. The DHA reductase and thioltransferase activities of GPX adds to the repertoire of functions of this enzyme as an important protector against cellular oxidative stress.
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