Apparent kinetic parameters for morphine-3-glucuronide formation catalyzed by microsomes of COS-1 cells expressing UGT2B7 alone and in combination with P450s
UGT activity was determined with five to six substrate concentrations up to 20 mM in the presence of 2 mM UDP-glucuronic acid. Data were fit to the Michaelis-Menten equation. Numbers in parentheses represent the value normalized to UGT2B7 singly expressed in COS-1 cells on the basis of UGT2B7 protein expression levels. Results are the estimated value ± S.D.
| Cells | Km | Vmax | Vmax/Km |
|---|---|---|---|
| mM | pmol / min / mg of protein | ||
| UGT2B7 | 0.38 ± 0.12 | 8.49 ± 0.20 (8.5) | 22.3 (22.3) |
| CYP3A4/UGT2B7 | 3.71 ± 0.68 | 7.23 ± 0.41 (9.47) | 1.9 (2.55) |
| CYP1A2/UGT2B7 | 0.48 ± 0.14 | 5.22 ± 0.17 (5.77) | 10.9 (12.0) |
| CYP2C9/UGT2B7 | 0.20 ± 0.12 | 4.43 ± 0.16 (4.3) | 22.2 (21.5) |