Reduction of the Ascorbyl Free Radical to Ascorbate by Thioredoxin Reductase

摘要: Recycling of ascorbic acid from its oxidized forms is required to maintain intracellular stores the vitamin in most cells. Since ubiquitous selenoenzyme thioredoxin reductase can recycle dehydroascorbic ascorbate, we investigated possibility that enzyme also reduce one-electron-oxidized ascorbyl free radical ascorbate. Purified rat liver catalyzed disappearance NADPH presence low micromolar concentrations were generated ascorbate by oxidase, and this effect was markedly stimulated selenocystine. Dehydroascorbic dismutation radical, However, control studies showed amounts under assay conditions used too account for observed loss NADPH. Electron paramagnetic resonance spectroscopy directly confirmed decreased steady-state concentrations, as expected if reduces radical. Dialyzed cytosol homogenates NADPH-dependent reduction Specificity indicated activity dialyzed prepared livers selenium-deficient rats, inhibition with aurothioglucose at selective reductase, stimulation Microsomal fractions substantial NADH-dependent not sensitive selenium depletion. These results suggest function a cytosolic may complement cellular recycling membrane-bound reductases.