Calculated kinetic parameters for codeine, fluoxetine and methadone biotransformations catalyzed by CYP2D6, HT-CYP2D6, HT-Cyp2d22, and CYP3A4 isoforms
Each data point used to calculate kinetic constants was based on an average of duplicate determinations. Enzyme Michaelis-Menten parameters and error estimates thereof were generated by nonlinear regression analysis (GraphPad Prism 3.02).
Reaction | P450 Isoform | Vmax | Km | Vmax/Km |
|---|---|---|---|---|
| pmol/pmol P450/min | μM | nl/pmol P450/min | ||
| CYP2D6 | 6.3 ± 0.3 | 180 ± 33 | 35 | |
| Codeine | HT-CYP2D6 | 3.7 ± 0.2 | 280 ± 44 | 13 |
| O-Demethylation | HT-Cyp2d22 | N.D. | ||
| CYP3A4 | N.D. | |||
| CYP2D6 | N.D. | |||
| Codeine | HT-CYP2D6 | N.D. | ||
| N-Demethylation | HT-Cyp2d22 | 3.8 ± 0.3 | 2200 ± 500 | 1.8 |
| CYP3A4 | 50 ± 1 | 620 ± 44 | 81 | |
| CYP2D6 | 0.53 ± 0.05 | 6.6 ± 1.3 | 84 | |
| Fluoxetine | HT-CYP2D6 | 0.38 ± 0.01 | 2.5 ± 0.2 | 150 |
| N-Demethylation | HT-Cyp2d22 | 0.75 ± 0.08 | 110 ± 29 | 6.8 |
| CYP3A4 | 0.20 ± 0.11 | 170 ± 24 | 1.2 | |
| CYP2D6 | N.D. | |||
| Methadone | HT-CYP2D6 | N.D. | ||
| N-Demethylation | HT-Cyp2d22 | 4.9 ± 0.5 | 520 ± 100 | 9.5 |
|
| CYP3A4 | 3.5 ± 0.01 | 33 ± 6 | 110 |
N.D., not detectable.