2007 Volume 24 Pages 42-48
A labile selenium donor compound, selenophosphate, is synthesized from selenide and ATP by selenophosphate synthetase (SPS). Selenophosphate is required by several bacteria and by mammals for the specific incorporation of selenium into selenoproteins and modified seleno-tRNAs. Although free selenide can be used in vitro for synthesis of selenophosphate, the physiological selenium substrate has not been identified. To identify the selenite-reducing system in E. coli, we constructed a gor mutant strain and a trxB mutant strain of E. coli MC4100. Active FDHH can be detected by monitoring benzyl viologen reduction. In the cells growing under fermentative condition on low-salt-medium in the absence formate at pH 7.5, the activity of FDHH was optimum. The wild-type strain MC4100 and the gor mutant strain were able to produce an active FDHH, but the trxB mutant strain failed to show FDHH activity. When ΔselD mutant strains were complemented by human lung Sps2Cys, the trxB mutant strain couldn’t generate active FDHH. We suggest that reduction of selenite in vivo is not dependent upon the glutathione-reducing system, but instead on the thioredoxin-reducing system.
