Table 1

Kinetic parameters of troglitazone glucuronidation in recombinant UGT isoforms and in human liver and jejunum microsomes

Microsomes	Eq. 1(Hyperbola)^1-a		Eq. 2(Substrate Inhibition)^1-b
Microsomes	K_m	V_max	V_max/K_m	K_m	V_max	V_max/K_m	K_i
	μM	pmol/min/mg	μl/min/mg	μM	pmol/min/mg	μl/min/mg	μM
Recombinant UGT1A1	58.3 ± 29.2	12.3 ± 2.5	0.21	141.1 ± 85.8	23.8 ± 9.9	0.17	220.4 ± 130.9
Recombinant UGT1A10	11.1 ± 5.8	33.6 ± 3.7	3.03	497.1 ± 2973.3	532.5 ± 2828.1	1.07	9.8 ± 54.7
Human liver microsomes (H161)	13.5 ± 2.0	34.8 ± 1.2	2.58	49.4 ± 26.3	70.2 ± 22.2	1.52	153.7 ± 76.3
Human jejunum microsomes (HJM0040)	8.1 ± 0.3	700.9 ± 4.3	86.53	62.7 ± 122.8	2138.5 ± 2990.4	34.11	58.6 ± 109.5

Troglitazone (6 μM–1 mM) was incubated with microsomes and UDP-glucuronic acid for 20 min.

↵1-a Kinetic parameters were calculated by the Michaelis-Menten equation (eq. 1) with the activity at 6–200 μM substrate concentrations.
↵1-b Kinetic parameters were calculated by the substrate inhibition equation (eq. 2) with the activity at 6 μM–1 mM substrate concentrations.