Table 3

Glucuronidation of opioids catalyzed by expressed human UGT1A3

SubstrateGlucuronide Formation
pmol/min/mg of protein
Morphinan opioids
 Morphine (5 mM)21  ± 6
 Hydromorphone (5 mM)14
 Nalorphine (5 mM)51
 Naloxone (2.5 mM)14
 Naltrexone (2.5 mM)38
 Codeine (5 mM)ND3-a
Oripavine opioids
 Buprenorphine (0.25 mM)55  ± 12
 Norburprenorphine (0.25 mM)130  ± 14
 Diprenorphine (0.25 mM)22
  • Assays were performed at pH 8.0 and 37°C for 0.5–1.0 hr, using whole-cell homogenates of HK293 cells expressing UGT1A3. The concentration of UDP-glucuronic acid was 2.0 mM, and the aglycone concentrations are indicated. Enzymatic rates are expressed as the mean ± SD of determinations from three transfections or the average determinations using cell homogenates from two transfections.

  • 3-a ND, glucuronide formation was not detected (limits of detection, 2.0 pmol/min/mg of protein).