Table 5

Kinetic parameters of EGCG and EGC glucuronidation by human UGTs expressed in insect cells

Human UGTs	EGCG-4 "-Gluc		EGCG-3 ′-Gluc		EGC-3 ′-Gluc
Human UGTs	V_max	K_m	V_max/K_m	V_max	K_m	V_max/K_m	V_max	K_m	V_max/K_m
	nmol/mg/min	μM	μl/mg/min	nmol/mg/min	μM	μl/mg/min	nmol/mg/min	mM	μl/mg/min
UGT1A1	0.98 ± 0.04	8.0 ± 1.3	123	0.17 ± 0.04	11.2 ± 1.0	15	0.50 ± 0.11	0.47 ± 0.15	1.1
UGT1A3	0.58 ± 0.05	53.6 ± 10.2	11	N/D	N/D	N/D	0.036 ± 0.013	1.49 ± 0.62	0.024
UGT1A8	5.59 ± 0.50	28.0 ± 8.0	200	N/D	N/D	N/D	0.12 ± 0.031	0.28 ± 0.14	0.41
UGT1A9	4.23 ± 0.41	31.0 ± 9.3	136	0.78 ± 0.09	24.2 ± 9.4	32	2.0 ± 0.13	0.20 ± 0.026	9.9

Kinetic studies were conducted for 15 min using 0.5 mg/ml of microsomal proteins from cells expressing human UGTs in the presence of UDPGA (1 mM) and with EGCG ranging from 2.5 to 150 μM or EGC ranging from 10 to 400 μM. The apparent kinetic parameters (K_mand V_max) of EGCG and EGC glucuronidation were calculated with GraphPad Prism 3.0. The values represent best-fit values ± standard error. V_max andK_m values were used to determine the catalytic efficiency (V_max/K_m).

N/D, not detectable.