Utilization of selenocysteine as a source of selenium for selenophosphate biosynthesis

Selenophosphate synthetase (SPS), the selD gene product from Escherichia coli , catalyzes the biosynthesis of monoselenophosphate from selenide and ATP. Characterization of selenophosphate synthetase revealed the determined K m value for selenide is far above the optimal concentration needed for growth and approached levels which are toxic. Selenocysteine lyase enzymes, which decompose selenocysteine to elemental selenium (Se 0 ) and alanine, were considered as candidates for the control of free selenium levels in vivo . The ability of a lyase protein to generate Se 0 in the proximity of SPS maybe an attractive solution to selenium toxicity as well as the high K m value for selenide. Recently, three E. coli NifS‐like proteins, CsdB, CSD, and IscS, were characterized. All three proteins exhibit lyase activity on L‐cysteine and L‐selenocysteine and produce sulfane sulfur, S 0 , or Se 0 respectively. Each lyase can effectively mobilize Se 0 from L‐selenocysteine for selenophosphate biosynthesis.