Cysteine peroxidase activity in rat blood plasma

Abstract

Early studies recognized that the human extracellular glutathione peroxidase may function cysteine peroxidase (cysteine:H₂O₂ oxidoreductase). The aim of the present study was the hypothesis of cysteine:H₂O₂ oxidoreductase activity in rat plasma. The rat plasma found to be able to accelerate greatly the H2O2-dependent oxidation of cysteine. The activity was a characteristic of a protein fraction precipitated at 30—44% ammonium sulfate saturation, and the specific activity in protein fraction was significantly higher than in plasma. Cysteine:H₂O₂ oxidoreductase reaction stoichiometry (2:1 mole ratio) was detected for the catalyzed interaction between cysteine and H2O2. Estimation of cysteine peroxidase activity may be useful in research on the functioning of the antioxidant system.

Keywords: aminothiol, stoichiometry; 5,5'-dithiobis(2-nitrobenzoic acid); Ellman's reagent