TABLE 2

Enzyme kinetic parameters determined by nonlinear regression for formation of M1 and M2 from (+)-tramadol and (−)-tramadol by dog recombinant P450s

ActivityP450High-Affinity ActivityLow-Affinity Activity
KmVmaxVmax/KmKmVmaxVmax/KmΣVmax/Km
μMpmol/min per pmol P450μl/min per nmol P450μMpmol/min per pmol P450μl/min per nmol P450
(+)-M1CYP2D155.51.0182662.132214
CYP2B111730.31.7
(−)-M1CYP2D153.00.1240591.32262
CYP2B114450.180.4
(+)-M2CYP2B1110.40.5484301.53.551.5
CYP2D154740.61.3
CYP2C21300.413
CYP2C418.51.1130
CYP3A12231.565
(−)-M2CYP2B117.20.2287651.92.530.5
CYP2D153510.61.7
CYP2C2168.50.34.4
CYP2C41610.813
CYP3A12550.47.3
  • The data points used for fitting were the average of three independent experiments performed in duplicate (data points shown in Fig. 5 with the curves of best fit). Fitted parameters included Km and Vmax, while intrinsic clearance (Vmax/Km) values were calculated. Data for (+)-M1 and (−)-M1 formation by CYP2D15 were best fit by a two-enzyme model. Kinetic parameters for high- and low-affinity activities, as well as the sum of the high and low intrinsic clearance values (ΣVmax/Km), are given.