Selenite can increase selenium-dependent glutathione peroxidase activity in glutathione- and glutathione reductase-deficient cells
It has been hypothesized that glutathione (GSH) and glutathione reductase (GRed) are essential for the reduction of selenite into the form of selenium (Se) necessary for incorporation into Se-dependent glutathione peroxidase (GPx). Human PC3 cells were made Se- and GPx-deficient by culturing them in 2.5% FBS (attaining GPx activity that was -5% of maximal GPx activity). These cells were then cultured without and with buthionine sulfoximine (BSO, 1 mM) to deplete GSH to 1.0% of normal. GPx activity of GSH-normal and -depleted PC3 cells increased to the same extent when cultured in the presence of selenite for four days, achieving GPx activity in that time that was ∼50% of maximum. GRed activity in GPx-deficient cells was decreased to 11.1% of normal by incubation with 1,3-bis(2-chloroethyl)nitrosourea (BCNU, 25 μM). GPx activity of GRed-normal and -deficient cells increased to the same extent when cultured in the presence of selenite for four days. GPx-deficient cells were depleted of both GSH and GRed by incubation with both BSO and BCNU. GSH levels were decreased to 1.1% of normal, and GRed activity was decreased to 38.5% of normal in these cells. GPx activity of GSH-/GRed-normal and -deficient cells increased to the same extent when cultured in the presence of selenite for four days. Thus selenite can increase GPx activity of GPx-deficient cells to the same extent even when GSH and GRed are decreased to very low levels. Therefore selenite can be incorporated into GPx by reductive mechanisms other than through GSH or GRed.
Bhamre, S; Whitin, JC; Cohen, HJ
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