TABLE 1

Selected probe substrate for each P450 and corresponding concentrations used in ISEF determination

P450	Probe Substrate	Isoform-Specific Metabolite	Substrate Concentration	HLM Conc.	rhP450 Conc.^{^a}
			μM	mg/ml	pmol/ml
1A2	Phenacetin^{^b}	O-Deethylation	0.5	0.5	76
2C8	Paclitaxel	6α-Hydroxylation	0.5	0.5	185
2C9	Diclofenac^{^b}	4-Hydroxylation	5	0.25	89
	S-Warfarin	7-Hydroxylation	0.5	0.5	179
	Tolbutamide	Hydroxylation	1	0.5	179
2C19	S-Mephenytoin	4-Hydroxylation	1	1.0	213
2D6	Bufuralol^{^b}	1-Hydroxylation	0.5	0.25	27
	Dextromethorphan	O-Demethylation	0.5	0.25	27
3A4	Midazolam^{^b}	1′-Hydroxylation	1	0.25	32
	Testosterone	6β-Hydroxylation	1	0.25	32
	Nifedipine	Hydroxylation	1	0.25	32

↵a Total protein concentration in rhP450 and HLM incubations was constant.
↵b Enzyme kinetics (K_m and V_max) were determined for CYP1A2, 2C9, 2D6, and 3A4 using these substrates.