Table 3

Kinetic parameters of EGCG glucuronidation in microsomes from human, mouse, and rat tissues

Microsomes	EGCG-4"-Gluc		EGCG-3′-Gluc		EGCG-7-Gluc
Microsomes	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	μM	μl/mg/min
Human liver	1.16 ± 0.06	272 ± 24	4.3	0.22 ± 0.01	236 ± 10	0.95	N/D	N/D	N/D
Rat liver	0.24 ± 0.01	145 ± 18	1.6	0.20 ± 0.02	115 ± 23	1.8	0.18 ± 0.02	399 ± 58	0.44
Mouse liver	1.80 ± 0.06	207 ± 15	8.7	0.78 ± 0.19	33 ± 33	24	Trace	Trace	Trace
Mouse small intestine	1.25 ± 0.19	70 ± 23	18.0	N/D	N/D	N/D	N/D	N/D	N/D

Kinetic studies were conducted for 30 min using 2 mg/ml of tissue microsomal proteins in the presence of 1 mM UDPGA and with EGCG concentrations ranging from 10 to 400 μM for liver microsomes and from 5 to 150 μM for small intestine microsomes. The formation of EGCG glucuronides was quantified with LC/MS/MS. The apparent kinetic parameters (K_m and V_max) of glucuronidation were calculated with GraphPad Prism. The values represent best-fit values ± standard error.V_max and K_m values were used to determine the catalytic efficiency (V_max/K_m). TheV_max and K_m values for EGCG-3′-Gluc in MLM were calculated with the first five data points.

N/D: not detectable.