Selenium-dependent glutathione peroxidase protein and activity: immunological investigations on cellular and plasma enzymes

Selenium-deficient humans and animals are known to be deficient in glutathione peroxidase (GSHPx) activity in their cells and plasma. To determine the relationship between enzyme activity and protein content, the enzyme was purified from human erythrocytes, and polyclonal antibodies were made against the purified protein in rabbits. These antibodies were found to be monospecific, noninhibitory, and capable of precipitating the enzymatic activity. All the GSHPx activity in erythrocytes and almost all the activity in neutrophils and platelets was precipitated by these antibodies. None of the plasma enzyme was precipitated by these antibodies, indicating that the plasma enzyme activity was attributable to a different selenium dependent protein moiety. Utilizing a radioimmunoassay, we were able to determine that there was a direct relationship between GSHPx activity and protein content in the erythrocytes of both normal and selenium-deficient individuals, and a similar relationship between control and selenium- deficient rat erythrocytes and liver cells. Thus, the ability to examine GSHPx as a protein resulted in two new observations concerning the selenium-dependent GSHPx. The first is that the plasma enzyme is antigenically distinct from the erythrocyte enzyme, and the second is that in the absence of selenium, there is a concomitant decrease in GSHPx protein.