Abstract: Recently it was shown that the presence of rat blood plasma (as well as of erythrocyte hemolysate) in the reaction mixture containing 43 mM Tris-HCl-buffer (pH 8.5), 0.29 mM EDTA, 19.2 mM sodium azide, 1 mM DL-homocysteine (Hcy), and 198 mM hydrogen peroxide (incubation at 37°C) results in a significant acceleration of the decrease in Hcy concentration caused by addition of H O . In this paper, we present data indicating that the observed activity is the homocysteine:H O -oxidoreductase (homocysteine peroxidase) activity. It has been found that the level of H O -dependent Hcy decrease observed in the presence of blood plasma corresponds to homocysteine:H O -oxidoreductase reaction stoichiometry of 2:1 (mole ratio). The activity observed belongs to the protein fraction isolated by saturation with ammonium sulfate to 50%; the specific activity in this protein fraction is significantly higher than that in the whole plasma. The results confirm the hypothesis that the reaction between Hcy and H O at the presence of plasma is catalyzed by the protein component of plasma and this is the homocysteine peroxidase reaction. This activity is not associated with serum albumin, which is known to function as thiol peroxidase, and probably belongs to extracellular glutathione peroxidase (Gpx3).
Reference: Razygraev A.V., Homocysteine peroxidase activity in rat blood plasma: stoichiometry and enzymatic character of the reaction, Biomeditsinskaya khimiya, 2013, vol: