Glucuronidation activities of human liver microsomes and human recombinant UGTs toward native warfarin and its hydroxylated derivatives. Glucuronidation activities UGT1A1, 1A3, 1A4, 1A6, 1A7, 1A8, 1A9, and 1A10 were measured using membrane fractions of recombinant UGTs expressed as His-tag proteins in baculovirus-infected Sf9 insect cells (5 μg). The substrate and cosubstrate (UDP-GlcUA) concentrations were 750 μM and 4 mM, respectively. Specific activities are expressed in micromolar per milligram of protein per minute and shown with S.E.s of the mean based on two experiments.