Table 2

Michaelis constants determined using product formation measurements and substrate depletion measurements for six P450 substrates

Product Formation2-bSubstrate Depletion2-b
TacrineCYP1A21-Hydroxylation2-a 2.81.4
ImipramineCYP2C19 N-Demethylation229.8
DextromethorphanCYP2D6 O-Demethylation0.440.30
ThioridazineCYP2D6 S-Oxidation0.120.12
MidazolamCYP3A41′-Hydroxylation2-a 1.00.52
  • 2-a  Reaction monitored in product formation experiments. Tacrine 2- and 4′-hydroxylation was also observed but product formed was less than the lower limit of quantitation. Midazolam 4-hydroxylation was also observed with aKM of 15 μM.

  • 2-b  Product formationKM values represent the mean of three determinations, substrate depletion the average of two determinations.