Table 2

Kinetic parameters for various CYP3A4 substrates in human lymphoblast-expressed CYP3A4 (mean ± S.E.)

CYP3A4 Substrate	Michaelis-Menten/Hill Equation		Two-Site Model
CYP3A4 Substrate	K_m/S₅₀	V_max	CL_int/CL_max	K_s	V_max	α	β
	μM	pmol/min/pmol P450	μl/min/pmol P450	μM	pmol/min/pmol P450
TST 6β-hydroxylation^2-a	42.7 ± 0.8	16.5 ± 0.2	0.22	93.5 ± 4.8	16.5 ± 0.2	0.15 ± 0.02
NIF oxidation^2-b	20.9 ± 2.2	9.7 ± 0.7	0.46	33.4 ± 4.9	12.8 ± 1.5		0.36 ± 0.08
FEL oxidation	26.4 ± 2.4	5.94 ± 0.23	0.22
SV 3′-hydroxylation	35.1 ± 3.4	13.4 ± 0.5^2-c
MDZ 1′-hydroxylation	3.5 ± 0.5	4.8 ± 0.2	1.37

↵2-a Sigmoidal kinetics, Hill coefficient = 1.34 ± 0.02, CL_max calculated as defined by Houston and Kenworthy (2000).
↵2-b Substrate inhibition, Ksi = 306 ± 55 μM, CL_int calculated asV_max/K_m ratio.
↵2-c Arbitrary number due to the lack of metabolic standards.