Table 2

Kinetic parameters of CBZ 10,11-epoxidation by expressed CYP3A4 and CYP3A7

Km1 (apparent)Km2(apparent)Vmax2Vmax2/Km2Km(apparent)VmaxVmax/Km
μM nmol/nmol P450/min μM nmol/nmol P450/min
CBZ only104.8248.323.640.0952720.90.500.0007
Plus AND12.8139.529.030.20806382.80.530.0014
Plus EST2.1666.924.760.03713616.70.150.0002
Plus DHEA-S80.9246.422.590.0917280.10.710.0025

Substrate concentrations were 15 to 500 μM. The reaction was performed in the absence or presence of 100 μM effectors.Km1, Km2, andVmax2 were calculated by a modified two-site equation (Vmax1 = 0) V = (Vmax2S2/Km1Km2)/(1 + S/Km1Km2) (Korzekwa et al., 1998)Km and Vmax were calculated from the Michaelis-Menten equation V =Vmax/(1 + (Km/S)).