Enzyme | Metabolite | From LC/MS Analysisa | From Radioactivity Detection | ||||||
---|---|---|---|---|---|---|---|---|---|
Km (mean ± S.E.) | Vmax (mean ± S.E.) (peak area ratio) | Vmax (mean ± S.E.)b | Vb | Vmax
b
| |||||
μM | |||||||||
HLM | M13 | 2.39 ± 0.23 | 3.62 ± 0.11c | ||||||
2.38 ± 0.23 | 340 ± 10d | 68 | 148e | ||||||
M23 | 2.80 ± 0.72 | 0.12 ± 0.009c | 20 | 48f | |||||
CYP3A4 | M13 | 1.34 ± 0.24 | 0.016 ± 0.0008c | ||||||
1.32 ± 0.24 | 1.5 ± 0.1 | 0.6 | 0.9 | ||||||
| M23 | 5.45 ± 0.98 | 0.0017 ± 0.0001c |
| 0.1 | 0.3 |
↵ a Kinetic values were estimated from extrapolation of Michaelis-Menten analysis.
↵ b Unit for V and Vmax is picomole per milligram of protein per minute and picomole per picomole P450 per minute for HLM and CYP3A4, respectively.
↵ c The values are the maximal peak area ratio of a metabolite to the internal standard (a relative Vmax value).
↵ d M13 formation activity was 3.15 pmol/pmol CYP3A4 in HLM/min based on CYP3A4 concentration of 108 pmol/mg in HLM (Rodrigues et al., 1999).
↵ e M13 formation activity was 1.37 pmol/pmol CYP3A4 in HLM/min based on CYP3A4 concentration of 108 pmol/mg in HLM (Rodrigues et al., 1999).
↵ f M23 formation activity was 0.44 pmol/pmol CYP3A4 in HLM/min based on CYP3A4 concentration of 108 pmol/mg in HLM (Rodrigues et al., 1999).