Reactive oxygen species-mediated oxidation of methionine residues inprotein results in a racemic mixture of R and S forms of methionine sulfoxide(MetO). MetO is reduced back to methionine by the methionine sulfoxidereductases MsrA and MsrB. MsrA is specific toward the S form and MsrB isspecific toward the R form of MetO. MsrB is a selenoprotein reported to containzinc (Zn). To determine the effects of dietary selenium (Se) and Zn on Msractivity, CD-1 mice (N=16/group) were fed, in a 2Ã2 design, diets containing0 or 0.2 μg Se/g and 3 or 15 μg Zn/g. As an oxidative stress, half of the mice received L-buthionine sulfoximine (BSO; ip; 2 mmol/kg, three times per weekfor the last 3 wk); the others received saline. After 9.5 wk, Msr (the combinedspecific activities of MsrA and MsrB) was measured in the brain, kidney, andliver. Se deficiency decreased (p<0.0001) Msr in all three tissues, but Zn hadno direct effect. BSO treatment was expected to result in increased Msr activity; this was not seen. Additionally, we found that the ratio of MetO tomethionine in liver protein was increased (indicative of oxidative damage) bySe deficiency. The results show that Se deficiency increases oxidation ofmethionyl residues in protein, that Se status affects Msr (most likely througheffects on the selenoprotein MsrB), and that marginal Zn deficiency has littleeffect on Msr in liver and kidney. Finally, the results show that the oxidativeeffects of limited BSO treatment did not upregulate Msr activity. [ABSTRACT FROM AUTHOR]