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Table 1 Kinetic analysis of UGT1A4-induced glucuronidation of tamoxifen, trans-4-hydroxytamoxifen and cis-4-hydroxytamoxifen

From: Characterization of tamoxifen and 4-hydroxytamoxifen glucuronidation by human UGT1A4 variants

Substrate UGT1A4 variant V max value (pmol/min/μg UGT1A4 protein) K m value (μM) V max/K m ratio (μl/min/μg UGT1A4 protein)
trans-4-Hydroxytamoxifen UGT1A424Pro/48Leu 62.4 ± 5.8 2.2 ± 0.4 29.3 ± 2.7
  UGT1A424Thr/48Leu 54.9 ± 11.4 1.6 ± 0.1 33.2 ± 4.9
  UGT1A424Pro/48Val 49.3 ± 2.8 1.2 ± 0.1* 40.8 ± 1.4**
cis-4-Hydroxytamoxifen UGT1A424Pro/48Leu 4.1 ± 0.1 2.1 + 0.4 2.0 + 0.3
  UGT1A424Thr/48Leu 5.0 + 0.7 2.3 + 0.4 2.2 + 0.5
  UGT1A424Pro/48Val 5.6 + 0.2 1.3 + 0.1 4.4 + 0.4
Tamoxifen UGT1A424Pro/48Leu 68.0 ± 8.6 2.0 ± 0.51 35.2 ± 9.6
  UGT1A424Thr/48Leu 62.1 ± 2.6 1.5 ± 0.20 41.0 ± 7.0
  UGT1A424Pro/48Val 52.1 ± 10.1 1.3 ± 0.10§ 40.1 ± 7.5
  1. Data are expressed as the mean ± standard deviation for three independent experiments. Values are significantly (*P = 0.01, **P = 0.005, P = 0.02, P = 0.001) or near-significantly (§ P = 0.053) higher than that observed for microsomes from wild-type UGT1A424Pro/48Leu-overexpressing cells.