Table 2

Kinetics of glucuronide formation for selected amines and opioids in HK293 cell homogenates expressing human UGT1A3

SubstrateExpressed UGT1A3Expressed UGT1A4
ApparentKMVmaxVmax/KMApparentKMVmaxVmax/KM
μM pmol/min/mg μl/min/mg (×100) μM pmol/min/mg μl/min/mg (×100)
Amines
 2-Aminobiphenyl1521, 163824, 352, 2472-a 450960
 4-Aminobiphenyl1362, 990219, 21516, 22662-a 570860
 Cyproheptadine267, 212172, 9664, 4581, 4351, 4763, 109
 Amitriptyline250, 28360, 5024, 18170, 12896, 6354, 49
 Imipramine514, 4308, 112, 33102-b 18058
Opioids
 Morphine3650, 291027, 490.7, 1.7NDa,c
 Buprenorphine61, 4885, 65139, 135ND2-a
 Norbuprenorphine16, 21110, 147690, 700ND2-a

  • Apparent KM values for the aglycone substrates were determined using 2.0 mM UDP-glucuronic acid. Other assay conditions are described in Materials and Methods. The optimal pH was used for each substrate, as follows: all amines, pH 8.4; buprenorphine, pH 7.0; morphine and norbuprenorphine, pH 8.0. Results are expressed as the values obtained using cell homogenates from two different transfections.

  • ↵2-a Data taken from Green and Tephly (1996).

  • ↵2-b Data taken from Green et al. (1995).

  • 2-c ND, compounds are not substrates.