Kinetic models and constants for 1NP glucuronidation by human UGT isoforms
Isoform | Empirical Modelsa, b, c | Two-Site Model | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Km or S50 | Vmax | nd | Ks | Vmax | αe | |||||
| μM | pmol/min · mg protein | μM | pmol/min · mg protein | |||||||
| 1A1c | 345 ± 9 | 260 ± 6 | 1.3 ± 0.1 | 647 ± 18 | 249 ± 5 | 0.18 ± 0.02 | ||||
| 1A3b, f | 1768 ± 524 | 102 ± 24 | 1978 ± 190 | 87 ± 5 | 0.35 ± 0.12g | |||||
| 1A4 | N.D. | |||||||||
| 1A6c | 3.1 ± 0.02 | 19,596 ± 74 | 1.3 ± 0.01 | 6.7 ± 0.2 | 19,646 ± 127 | 0.22 ± 0.02 | ||||
| 1A7c | 1.4 ± 0.1 | 74 ± 2 | 2.3 ± 0.3 | 8.0 ± 0.9 | 77 ± 2 | 0.03 ± 0.01 | ||||
| 1A8c | 87 ± 6 | 1011 ± 37 | 1.5 ± 0.1 | 267 ± 84 | 1023 ± 37 | 0.11 ± 0.07 | ||||
| 1A9c | 1.3 ± 0.1 | 35 ± 0.8 | 2.2 ± 0.2 | 10 ± 1 | 37 ± 1 | 0.02 ± 0.004 | ||||
| 1A10a | 2.0 ± 0.1 | 1293 ± 26 | ||||||||
| 2B7c | 107 ± 5 | 44 ± 1 | 2.0 ± 0.2 | 668 ± 57 | 46 ± 1 | 0.03 ± 0.005 | ||||
| 2B15, 2B17 | N.D. |
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N.D., not determined.
↵ a Michaelis-Menten, b Substrate inhibition, c Hill equation.
↵ d Hill equation coefficient.
↵ e Interaction factor from two-site model. β = 2, except for UGT1A3 since Vmax is equivalent to 2Kp[E]t for autoactivation (where [E]t is the total enzyme concentration).
↵ f Ksi = 938 ± 303 μM.
↵ g β = 0.11 ± 0.04.