Table 1

A summary of the reaction conditions and Michaelis-Menten parameters of drug biotransformation reactions used as selective probes for human cytochrome P450 in vitro

CYP (Enzyme Activity)Reaction Conditions (Linear Range)Michaelis-Menten ParametersSubstrate (Concentration in Assay)
Time (min)Protein conc. (mg/ml)Liver IDKm(μM)Vmax (nmol/min/mg)
HL1391349  ± 330.255  ± 0.003
1A220  (0–20)0.5  (0.25–2.0)HL1401565  ± 590.110  ± 0.001Caffeine
Caffeine N3-demethylationHL141587  ± 270.295  ± 0.005 (1000 μM)
Mean1167  ± 514
HL1391.06  ± 0.090.224  ± 0.003
2A65  (0–15)0.025  (0.025–0.2)HL1400.82  ± 0.130.564  ± 0.040Coumarin
Coumarin 7-hydroxylationHL1410.81  ± 0.060.259  ± 0.005 (5 μM)
Mean0.90  ± 0.14
HL139348  ± 250.419  ± 0.014
2C930  (0–30)0.5  (0.25–1.0)HL140133  ± 20.434  ± 0.006Tolbutamide
Tolbutamide hydroxylationHL141137  ± 30.387  ± 0.027 (100 μM)
Mean206  ± 123
HL13975.8  ± 16.70.066  ± 0.007
2C1930 or 60  (0–60)1.0  (0.25–1.0)HL140ND S-Mephenytoin
S-Mephenytoin 4-hydroxylationHL14129.5  ± 0.80.055  ± 0.002 (75 μM)
Mean52.71-a
HL1392.19  ± 0.040.552  ± 0.007
2D651-b  (0–30)0.25  (0.05–0.4)HL1408.48  ± 1.790.097  ± 0.008Dextromethorphan
DextromethorphanO-demethylationHL1412.18  ± 0.060.566  ± 0.012 (5 μM)
Mean4.3  ± 3.6
HL13964.2  ± 4.03.78  ± 0.08
2E110  (0–40)0.25  (0.05–0.4)HL14055.1  ± 7.35.59  ± 0.45Chlorzoxazone
Chlorzoxazone 6-hydroxylationHL14151.0  ± 3.42.75  ± 0.03 (50 μM)
Mean56.8  ± 6.8
HL139148  ± 182.07  ± 0.03
3A4/530  (0–30)0.25  (0.05–0.4)HL140133  ± 190.33  ± 0.02Dextromethorphan
DextromethorphanN-demethylationHL141369  ± 142.89  ± 0.04 (500 μM)
Mean217  ± 132
  • 1-a Mean of two livers.

  • 1-b The time indicated was used for microsomes prepared from HL139 and HL141. Due to the low dextromethorphanO-demethylation activity of HL140 microsomes, we used a 30 min reaction time for this liver. ND, not determined.