Reverse phase-HPLC chromatograph of product ion (m/z 501) experiments. Tracings represent organic-soluble metabolites generated during incubation of human liver microsomes with UDP-glucuronic acid (4 mM) and 750 μM of each substrate (green, 4′-hydroxywarfarin; red, 6-hydroxywarfarin; blue, 7-hydroxywarfarin; black, 8-hydroxywarfarin; pink, 10-hydroxywarfarin). No specific metabolites were generated when 10-hydroxywarfarin (750 μM), racemic warfarin (750 μM), (S)-warfarin (750 μM), or (R)-warfarin (750 μM) were used as substrates (data not shown). Each substrate was incubated individually for 180 min. All other incubation conditions are noted under Materials and Methods.