Kinetic parameters of malathion desulfuration by recombinant human P450s
Km and Vmax data are expressed as mean ± S.D. from at least three determinations.
P450 | Vmax | Km | CLi (Vmax/Km) | Percentage Contributiona |
|---|---|---|---|---|
| nmol malaoxon · (nmol P450 · min)-1 | μM | ml · (nmol P450 · min)-1 | ||
| 2C19 | 5.00 ± 0.01 | 0.445 ± 0.004 | 11.2 | 14.2 |
| 1A2 | 3.67 ± 0.03 | 0.78 ± 0.04 | 4.7 | 83.5 |
| 2B6 | 3.6 ± 0.2 | 3.09 ± 0.07 | 1.1 | 0.3 |
| 1A1 | 1.0 ± 0.2 | 11.8 ± 0.1 | 0.09 | N.D. |
| 3A4 | N.D. | N.D. | 0.025b | 1.6 |
| 2C9 | N.D. | N.D. | 0.017b | 0.3 |
| 2C8 | N.D. | N.D. | 0.015b | 0.1 |
N.D., not determined.
↵ a Values of the relative contributions (percentage) to total malathion desulfuration were calculated from CLi values of the active P450s, taking into account the average human hepatic content of each isoform (1A2, 12%; 3A4, 40%; 2C19, 1.1%; 2B6, 0.2%; 2C8, 5.4%; 2C9, 9.4%; 1A1, traces) as reported in Rendic and Di Carlo (1997).
↵ b CLi values represent the slope of the linear enzymatic activity.