As a first step in library screening, we found an SeO3 2-culture concentration in which cells expressing WT-GRMLR could consistently outcompete cells expressing a disabled GRLMR enzyme. Like its highly characterized parent analogue GSHR, GRLMR contains a cysteine-based disulfide which is described as the putative active site. In GRLMR, SeR, and GSHR, among others, the active site sequence motif is CXXXXC. In GRLMR, the active site cysteine residues are C42 and C47.