When hemolyzates from erythrocytes of selenium-deficient rats were incubated in vitro in the presence of ascorbate or H(2)O(2), added glutathione failed to protect the hemoglobin from oxidative damage. This occurred because the erythrocytes were practically devoid of glutathione-peroxidase activity. Extensively purified preparations of glutathione peroxidase contained a large part of the (75)Se of erythrocytes labeled in vivo. Many of the nutritional effects of selenium can be explained by its role in glutathione peroxidase.

Experiments were conducted with male rats to quantitate the relation ship between dietary selenium (Se) intake and the amount of the enzyme glutathione peroxidase (GSH-Px) in erythrocytes and liver. Weanling male rats were fed torula yeast-based diets with 0, 0.05, 0.1, 0.5, 1.0, or 5.0 ppm Se supplemented as sodium selenite. Liver GSH-Px fell to undetectable levels (<1% of that found in the weanling rats) within 24 days in the O ppm Se group; feeding 0.1 ppm Se, or greater, caused liver GSH-Px to increase above that found in the weanling rats. The erythrocyte GSH-Px response to lack of dietary Se was somewhat smaller in magnitude and more gradual; however, only 21% of initial erythrocyte GSH-Px activity remained in the unsupplemented group after 66 days. Increased dietary Se resulted in corresponding increases of erythrocyte GSH-Px activity. Resupplementing with 0.1, 0.5, or 5.0 ppm Se elevated the depressed erythrocyte GSH-Px levels of the deficient rats. Increased dietary Se provided for both faster elevation, and higher maximal GSH-Px activity which in all cases was achieved 60 to 90 days after resupplementation. The results suggest that tissue GSH-Px can be used as an indicator of animal Se status, but other factors such as age, sex, and dietary vitamin E may have to be considered. Lack of GSH-Px in livers of Se-deficient rats may explain the liver necrosis observed when the diet is also deficient in vitamin E and sulfur-containing amino acids.

Numerous biochemical reactions can be measured potentiometrically through changes in pH, redox potential, or transmembrane potential. An alternating photocurrent through an electrolyte-insulator-semiconductor interface provides a highly sensitive means to measure such potential changes. A spatially selectable photoresponse permits the determination of a multiplicity of chemical events with a single semiconductor device.

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