A Comparative Study on the Hydroperoxide and Thiol Specificity of the Glutathione Peroxidase Family and Selenoprotein P

Abstract

Glutathione peroxidase catalyzes the reduction of hydrogen peroxide and organic hydroperoxide by glutathione and functions in the protection of cells against oxidative damage. Glutathione peroxidase exists in several forms that differ in their primary structure and localization. We have also shown that selenoprotein P exhibits a glutathione peroxidase-like activity (Saito, Y., Hayashi, T., Tanaka, A., Watanabe, Y., Suzuki, M., Saito, E., and Takahashi, K. (1999) J. Biol. Chem. 274, 2866 -2871). To understand the physiological significance of the diversity among these enzymes, a comparative study on the peroxide substrate specificity of three types of ubiquitous glutathione peroxidase (cellular glutathione peroxidase, phospholipid hydroperoxide glutathione peroxidase, and extracellular glutathione peroxidase) and of selenoprotein P purified from human origins was done. The specific activities and kinetic parameters against two hydroperoxides (hydrogen peroxide and phosphatidylcholine hydroperoxide) were determined. We next examined the thiol specificity and found that thioredoxin is the preferred electron donor for selenoprotein P. These four enzymes exhibit different peroxide and thiol specificities and collaborate to protect biological molecules from oxidative stress both inside and outside the cells.

Metformin Suppresses Expression of the Selenoprotein P Gene via an AMP-activated Kinase (AMPK)/FoxO3a Pathway in H4IIEC3 Hepatocytes

“…Measurement of Glutathione Peroxidase Activity-To measure cellular glutathione peroxidase (cGPx) activity, a coupled enzyme assay, which was performed by following the oxidation of NADPH, was used as described previously (22). In brief, cells were cultured with 1) DMEM plus 10% FBS, 2) DMEM plus 10% FBS and 100 nM selenious acid, or 3) DMEM plus 10% FBS and 1000 nM selenious acid at 72 h. Then cells were fractured with homogenate buffer containing 0.25 M sucrose, 50 mM Tris-HCl (pH 7.4), 0.1 mM EDTA, 0.1 mM 2-mercaptoethanol.…”

Selenium and asthma: a complex relationship

“…There are, in fact, five human GPX selenoenzymes: GPX1-4 and 6. In addition to the GPX enzymes, other selenoproteins to which antioxidant or redox properties have been attributed include thioredoxin reductase-1, -2 and -3 as well as selenoproteins H, P, R and W (12)(13)(14)(15). A total of 25 selenoproteins have been identified in humans, 24 of which exist as selenoproteins in rodents (16).…”

Selenium‐containing amino acids as direct and indirect antioxidants

“…However, phospholipid hydroperoxide glutathione peroxidase activity has been reported for this protein with a catalytic mechanism similar to that of GPx. Multiple thiol-containing molecules, including Trx, Cys, homocysteine, and DTT can act as electron donors for selenoprotein P, compensating for the low extracellular GSH levels (51,52).…”