Enzyme kinetic parameters for midazolam 1’-hydroxylation in pooled human liver microsomes and heterologously expressed cytochrome P4503A4
Values in parenthesis represent the 95% confidence interval of the data fitting.
| Reagent | KM (µM) | Vmax (pmol/min/x)a | CLint,u (µL/min/x)b | CYP abundance (pmol/mg microsomal protein) | ISEF | ||
|---|---|---|---|---|---|---|---|
| Experiment 1 | HLM | 1.62 (1.34 - 1.98)c | 852 (787 - 930) | 525 | 137 | 0.23 | |
| rCYP3A4 | 0.412 (0.359 - 0.473)c | 6.73 (6.46 - 7.03) | 16.3 | ||||
| Experiment 2 | HLM | 1.37 (1.02 - 1.84) | 646 (597 - 699) | 472 | 137 | 0.29 | |
| rCYP3A4 | 0.448 (0.362 - 0.552)c | 5.35 (5.02 - 5.71) | 11.9 | ||||
| Arithmetic Mean | 0.26 | ||||||
aVmax units are pmol/min/mg for human liver microsome and pmol/min/pmol P450 for heterologously expressed individual P4503A4.
bClint units are µL/min/mg for human liver microsome and µl/min/pmol P450 for heterologously expressed individual P4503A4; midazolam fumic = 1 for both human liver microsome and heterologously expressed individual P4503A4.
cData fit to substrate inhibition model, resulting substrate inhibition (Ki) values were > 100 µM (3 times the highest substrate concentration tested).