Kinetic parameters for 4-methylumbelliferone, SN-38, and 17β-estradiol (3-hydroxy group) glucuronidation catalyzed by UGT1A1*1 and its allelic variant *6: effect of CYP3A4 cotransfection
Data were fitted to a Michaelis-Menten equation. Results are the estimated value ± S.E.
| UGT1A1 and a variant | S50 | Vmax | Hill coefficient |
|---|---|---|---|
| µM | pmol/min/mg protein | n | |
| 4-MUa | |||
| *1 | 58.8 ± 4.1 | 385 ± 13 | 1.5 ± 0.1 |
| *1+CYP3A4 | 53.6 ± 2.7 | 534 ± 13$$$ | 1.6 ± 0.1 |
| *6 | 122 ± 13¶¶¶ | 211 ± 12¶¶ | 1.7 ± 0.3 |
| *6+CYP3A4 | 124 ± 11 | 413 ± 20$$$ | 1.9 ± 0.3 |
| SN-38b | |||
| *1 | 14.0 ± 0.3 | 28.6 ± 0.2 | 1.35 ± 0.03 |
| *1+CYP3A4 | 16.6 ± 0.3$$$ | 51.1 ± 0.4$$$ | 1.25 ± 0.02$$ |
| *6 | 18.1 ± 0.6¶¶ | 7.1 ± 0.1¶¶¶ | 1.48 ± 0.06 |
| *6+CYP3A4 | 30.4 ± 1.1$$$ | 18.9 ± 0.4$$$ | 1.34 ± 0.03 |
| 17β-estradiolc | |||
| *1 | 60.0 ± 1.4 | 150 ± 2 | 3.8 ± 0.3 |
| *1+CYP3A4 | 65.9 ± 1.9 | 231 ± 4$$$ | 3.6 ± 0.3 |
| *6 | 102 ± 2¶¶¶ | 35.1 ± 0.6¶¶¶ | 5.2 ± 0.5 |
| *6+CYP3A4 | 106 ± 1 | 66.3 ± 0.7$$$ | 5.4 ± 0.3 |
↵a UGT activity was determined in the presence of 2 mM UDP-GlcUA with 10 substrate concentrations ranging from 10 to 500 µM (UGT1A*1) and from 20 to 800 µM (UGT1A1*6);
↵b Ranging from 2 to 100 µM;
↵c Ranging from 8 to 500 µM (UGT1A*1) and from 10 to 500 µM (UGT1A1*6).
¶¶ P < 0.001, ¶¶¶P < 0.0001 from *1; $P = 0.018, $$P < 0.001, $$$P < 0.0001 from single expression.