Combined, this analysis shows the enzyme evolving towards a broad capacity to use selenium as a preferred substrate, instead of GS-Se-SG which is preferred by the parent enzyme . This could imply that at very high concentrations of selenite (50mM in liquid culture), intracellular concentrations of selenite may exceed the usual form of intracellular selenium (GS-Se-SG), resulting in selective pressure for enzymes preferring SeO3 2-over GS-Se-SG.