Enzyme kinetic constants and estimated contribution of various CYPs to the metabolic clearance of siponimod in human liver microsomes
Enzyme kinetic parameters Vmax and Km of CYP3A4 and CYP2C9 were obtained from kinetic experiments. The values of other isoenzymes were estimated by solving the Michaelis-Menten equation for the two concentrations of substrate and their rate numbers.
| Enzyme | Km (µM) | Vmax (pmol/(min·nmol CYP) | CL (Vmax/Km) µl/(min.·nmol CYP) | Abundance (pmol P450/mg)a | Specific concentration (% Total CYP) | Relative CL µl/(min. nmol Total CYP) | Contribution (% Total Relative CL) |
|---|---|---|---|---|---|---|---|
| CYP1A2 | 52 | 9.47% | |||||
| CYP2A6 | 36 | 6.56% | |||||
| CYP2B6 | 40.0 | 88.9 | 2.2 | 11 | 2.00% | 0.04 | 0.4% |
| CYP2C8 | 2.9 | 14.3 | 5 | 24 | 4.37% | 0.22 | 1.7% |
| CYP2C9 | 34.5 | 2596 | 75.2 | 73 | 13.30% | 10.01 | 79.2% |
| CYP2C19 | 140 | 100 | 0.7 | 14 | 2.55% | 0.02 | 0.1% |
| CYP2D6 | 8 | 1.46% | |||||
| CYP2E1 | 61 | 11.11% | |||||
| CYP3A4b | 85.1 | 706 | 8.3 | 155 | 28.23% | 2.34 | 18.5% |
| Total | 434 | 79% | 12.63 | 100% |