American Journal of Clinical Nutrition, Vol 27, 995-1004, Copyright © 1974 by The American Society for Clinical Nutrition, Inc.

Possible stabilizing effect of vitamin E on microsomal, membrane-bound, selenide-containing proteins and drug-metabolizing enzyme systems

¹ From the Department of Biochemistry, Royal Free Hospital, School of Medicine, University of London, 8, Hunter Street, WCIN 1BP, United Kingdom

Recent work in our laboratory has indicated that a biologically active form of selenium in rat liver may be selenide, which can be derived by an intracellular mechanism from administered Na₂ ⁷⁵ SeO₃. It has been demonstrated that the selenide is protein bound, is particularly located in subcellular loci that have an electron-transport function (namely, mitochondria and smooth endoplasmic reticulum), and that the presence of substantial amounts of selenide in rat liver subcellular organelles is dependent on the presence of vitamin E in the diet of the animals. In the present communication, further studies on the selenide of rat liver smooth endoplasmic reticulum will be presented. It will be shown that the inductive effect of phenobarbitone on the microsomal drug-metabolizing enzyme system of normal rats is accompanied by a large increase in the uptake of selenium and its conversion to selenide; when vitamin E is withdrawn from the diet, this effect cannot be demonstrated. Investigation of the amounts of the cytochrome constituents of the microsomal system showed that their biosynthesis was unimpaired in vitamin E deficiency, and kinetic studies on the NADH and NADPH cytochrome c and of the extent of reduction of the cytochromes by the reduced pyridine nucleotides, gave results indistinguishable from controls. When, however, the drug-metabolizing activity of microsomes of vitamin E-deficient rat liver was examined, it was found that their demethylating capacity was impaired. The hypothesis will be discussed that the selenide forms part of the active center of a microsomal non-heme iron-containing protein, and results will be presented showing that oxidant-labile non-heme iron can be detected in the livers of normal rats. Consideration will be given to the view that vitamin E may function by protecting selenide-containing non-heme iron proteins from oxidation in vivo, partly by virtue of its membrane-stabilizing ability and partly through its antioxidant function.