Peroxide removal by selenium-dependent and selenium-independent glutathione peroxidases in hemoglobin-free perfused rat liver.

Two glutathione peroxidase activities have been described in rat liver. One contains selenium and is virtually absent in selenium deficiency. The other seems to be unaffected by selenium status. The selenium-dependent glutathione peroxidase utilizes H,O, and organic hydroperoxides as substrates, but the selenium-independent glutathione peroxidase is much more efficient with organic hydroperoxide substrates than with H,O,. The purpose of these experiments was to evaluate the function of these glutathione peroxidase activities in the intact organ. Selenium-deficient livers contained the following percentages of control per g: glutathione peroxidase with H,O, as substrate, 5%; glutathione peroxidase with tert-butyl hydroperoxide as substrate, 29%; glutathione reductase, 91%; glutathione, 106%; glucose-& phosphate dehydrogenase, 63%; and catalase, 244%. The function of glutathione peroxidase in the intact organ was studied using a hemoglobin-free liver perfusion system. Release of GSSG into the effluent in response to peroxide infusion was taken as evidence of glutathione peroxidase function. Infusion of H,O, into control livers caused release of GSSG which was proportional to the H,O, infusion rate. In contrast, selenium-deficient livers released no GSSG in response to even the highest H,O, infusion rates. Both selenium-deficient and control livers released GSSG in response to tert-butyl hydroperoxide infusion. These results indicate the presence of a selenium-independent glutathione peroxidase which removes organic hydroperoxides in the intact liver but which does not function in H,O, removal, at least under the present experimental conditions. They provide evidence that the selenium-independent glutathione peroxidase recently described in rat liver can function in the intact organ.