Table 3.
Apparent enzyme kinetics for glucuronidation and sulfation of ABT-751
| Microsomes or isoforms | Km (μmol/l) (mean±SE) | Vmax (pmol/min/mg) (mean±SE) | Vmax (U/mg protein)a (mean±SE) | Vmax/Km (μl/min/mg) (unnormalized) | Relative level of expressed proteinb | Relative Vmax | Relative Vmax/Km (μl/min/mg) (normalized) |
|---|---|---|---|---|---|---|---|
| Pooled HLM | 114.2±16.2 | 150.9±6.5 | – | 1.3 | – | – | – |
| UGT1A1 | 82.8±7.8 | 60.0±1.7 | – | 0.7 | 0.4 | 150.0 | 1.8 |
| UGT1A4 | 43.3±5.3 | 54.3±1.5 | – | 1.3 | 0.6 | 90.5 | 2.2 |
| UGT1A8 | 36.7±7.1 | 141.9±5.7 | – | 3.9 | 1 | 141.9 | 3.9 |
| UGT2B7 | 58.4±4.5 | 41.8±0.8 | – | 0.7 | – | – | – |
| SULT1A1*1 | 88.4±18.0 | – | 25.3±2.7 | – | – | – | – |
| SULT1A1*2 | 164.8±16.7 | – | 5.4±0.4 | – | – | – | – |
| SULT1A1*3 | 109.0±8.3 | – | 3.7±0.2 | – | – | – | – |
| SULT2B1b | 120.6±6.4 | – | 0.8±0.002 | – | – | – | – |
HLM, human liver microsomes; Km, Michaelis constant; SULT, sulfotransferase; UGT, uridine 5′-diphosphoglucuronosyltransferase; Vmax, maximum velocity.
a
One unit of enzyme activity represents the formation of 1 nmol of acceptor sulfate per hour of incubation at 37°C.
b
The expression of UGT1A8 was expressed arbitrarily as the basal UGT1A expression level.