The mouse DAO cell assay routinely employed CHO-K1 cells, which were transiently transfected with an expression plasmid containing the mouse DAO nucleotide encoding the full-length mouse DAO protein. The CHO-K1 cell line was routinely cultured in Gibco Ham's F-12 Nutrient Mix containing 10% FBS. The mouse DAO cell assay was performed using the following final assay conditions: 35,000 CHO-K1 cells transiently transfected with mouse DAO/ pcDNA3.1+C_(K)-DYK expression plasmid, 50 mM D-Serine, 50 µM Amplex Red and 0.125 U/mL HRP. All cells and reagents were made up in 10 mM HEPES buffer. The final assay volume was 25 µL/well.