Kinetic parameters of ebastine hydroxylation by recombinant P450 4F enzymes and liver microsomes from marmosets, cynomolgus monkeys, and humans
Kinetic parameters were determined by nonlinear regression analysis (mean ± S.E., n = 16 points of substrate concentrations of 0.4–500 μM). Values are based on duplicate determinations. Recombinant P450 protein and intestinal microsomes were incubated with ebastine of optional concentrations for 30 minutes at 37°C in the presence of an NADPH-generating system.
| Enzyme Source | Km | Vmax | Vmax | Vmax/Km | Vmax/Km |
|---|---|---|---|---|---|
| μM | nmol/min per nmol P450 | pmol/min per mg | ml/min per nmol | μl/min per mg | |
| P450 form | |||||
| Marmoset 4F12 | 40 ± 8 | 7.6 ± 1 | 0.19 | ||
| Cynomolgus monkey 4F12 | 5.2 ± 0.7 | 2.9 ± 0.1 | 0.56 | ||
| Human 4F12 | 5.9 ± 0.8 | 2.4 ± 0.1 | 0.41 | ||
| Microsome | |||||
| Marmoset intestine | 18 ± 4 | 797 ± 47 | 44 | ||
| Cynomolgus monkey intestine | 54 ± 14 | 1230 ± 103 | 23 | ||
| Human intestine | 6.4 ± 0.6 | 124 ± 2 | 19 |