Apparent kinetic parameters for the glucuronidation of entacapone and tolcapone by human recombinant UGT isoforms and human liver microsomes (HLM). The values represent mean ± S.D. of two to five determinations (standard deviation shown when n = 3–5).
| UGT Source | Entacapone | Tolcapone | ||||
|---|---|---|---|---|---|---|
| Vmax | Km | Vmax/Km | Vmax | Km | Vmax/Km | |
| nmol min−1 mg−1 | μM | ml min−1 mg−1 × 10− 3 | ||||
| UGT1A12-a | 0.004 | 31 | 0.13 | |||
| 0.005 | 93 | 0.05 | ||||
| UGT1A9 | 1.8 ± 0.6 | 10.0 ± 1.9 | 182 | 0.48 ± 0.15 | 66 ± 12.0 | 7.3 |
| UGT2B15 | 0.024 | 322 | 0.08 | 0.024 | 429 | 0.06 |
| HLM | 6.8 ± 2.0 | 47 ± 5 | 144 | 2.1 ± 1.1 | 201 ± 102 | 10.3 |
↵2-a Two glucuronides detected. The UGT1A1 kinetic data listed first corresponds to the 3-O-glucuronide (Fig. 2).