Apparent enzyme kinetic parameters for 4-OH-Cy formation by different microsome batches with recombinant CYP2B6*1 and different POR/CYP ratios.

* POR measured as Cytochrome c reductase activity as in Table 1** Vmax is based on 4-OH-Cy formedCLint Calculated as Vmax/KmCyclophosphamide at different concentrations was incubated in 2 independent experiments with 3 batches of CYP2B6.1 containing different POR/CYP ratios. The 4-OH-Cy formation, used as a measure of Cy metabolism, was measured using HPLC. The results shown are the averages obtained for each of the three batches. The results show almost proportional increase of Cy intrinsic clearance (i.e. apparent Vmax/Km, with Vmax measured from 4-OH-Cy formation) with higher POR/CYP ratios from Batch 1 to Batch 3.