Demonstration of Glutathione Peroxidase in Rat Liver Peroxisomes and Its Intraorganellar Distribution

Earlier, we reported that rat liver peroxisomes contain Cu-Zn superoxide dismutase (J. Biol. Chem. 267, 6870), thereby suggesting a new antioxidant role for this organelle in free radical metabolism. In this study, we report for the first time that mammalian peroxisomes also contain glutathione peroxidase. Using highly purified rat liver peroxisomes isolated by Nycodenz gradient, we found that peroxisomes contain glutathione peroxidase which shows enzymatic activity with different substrates such as hydrogen peroxide, cumene hydroperoxide, and t-butyl hydroperoxide. This activity could be inhibited in vitro by mercaptosuccinate. Western blot analysis revealed that peroxisomes from control and ciprofibrate-treated livers show immunoreactive bands with antibodies raised against glutathione peroxidase. The intraperoxisomal distribution of glutathione peroxidase was investigated by using peroxisomal membrane and matrix proteins. The results revealed that glutathione peroxidase is a matrix enzyme. The presence of glutathione peroxidase in peroxisomes provides an alternate enzyme system responsible for the degradation of organic peroxides and the degradation of H2O2 under conditions in which catalase is inactivated (e.g., ischemia-reperfusion and endotoxemia). These findings suggest that glutathione peroxidase in peroxisomes may play a novel role in the cellular antioxidant responses to various oxidative stress conditions.