Ubiquinone is reduced by lipoamide dehydrogenase and this reaction is potently stimulated by zinc

AbstractUbiquinol is an endogenously synthesized lipid-soluble antioxidant. Regeneration of ubiquinol from the oxidized form is essential to the maintenance of its antioxidant function. We demonstrated that lipoamide dehydrogenase can reduce ubiquinone to ubiquinol. Zinc increased the rate of the NADPH-dependent reduction more than 10-fold. The concentration ubiquinone resulting in the half-maximal rate of reduction was approximately 5 μM in the presence and 4 μM in the absence of zinc. These data may explain how ubiquinone is reduced to the active antioxidant ubiquinol, which plays such an important role in protecting against oxidative stress and lipid peroxidation

Overexpression of Enzymatically Active Human Cytosolic and Mitochondrial Thioredoxin Reductase in HEK-293 Cells. Effect on cell growth and differentiation

8 páginas, 5 figuras, 1 tabla.The mammalian thioredoxin reductases (TrxR) are selenoproteins containing a catalytically active selenocysteine residue (Sec) and are important enzymes in cellular redox control. The cotranslational incorporation of Sec, necessary for activity, is governed by a stem-loop structure in the 3'-untranslated region of the mRNA and demands adequate selenium availability. The complicated translation machinery required for Sec incorporation is a major obstacle in isolating mammalian cell lines stably overexpressing selenoproteins. In this work we report on the development and characterization of stably transfected human embryonic kidney 293 cells that overexpress enzymatically active selenocysteine-containing cytosolic TrxR1 or mitochondrial TrxR2. We demonstrate that the overexpression of selenium-containing TrxR1 results in lower expression and activity of the endogenous selenoprotein glutathione peroxidase and that the activity of overexpressed TrxRs, rather than the protein amount, can be increased by selenium supplementation in the cell growth media. We also found that the TrxR-overexpressing cells grew slower over a wide range of selenium concentrations, which was an effect apparently not related to increased apoptosis nor to fatally altered intracellular levels of reactive oxygen species. Most surprisingly, the TrxR1- or TrxR2-overexpressing cells also induced novel expression of the epithelial markers CK18, CK-Cam5.2, and BerEP4, suggestive of a stimulation of cellular differentiation.This work was supported by Åke Wibergsstiftelse, Karolinska Institutet, Södertörns Högskola, and the Swedish Medical Research Council Projects 13X-10370, 03P-14096-01A, and 03X-14041-01A.Peer reviewe