Table 2

Kinetic parameters for raloxifene glucuronidation by expressed UGTs, human liver, and intestinal microsomes

	R-6-G		R-4-G
	K_m	V_max	Cl_int	K_m	V_max	Cl_int
	μM	nmol/min/mg	μl/min/mg	μM	nmol/min/mg	μl/min/mg
UGT 1A1	—^2-a	—^2-a	—^2-a	—^2-a	—^2-a	—^2-a
UGT 1A8	7.9	0.61	77	59	2.0	34
UGT 1A9	25	0.32	12	13	0.25	19
UGT 1A10	N.D.^2-b	N.D.	N.D.	4.8^2-c	0.55^2-c	115^2-c
Human liver microsomes	—^2-a	—^2-a	—^2-a	46	1.5	32
Human jejunum microsomes	58	0.99	17	54	5.1	95

Expressed UGT1A8 (25 μg), 1A1, 1A9, and 1A10 (50 μg) or human liver and jejunum microsomes (25 μg) were pretreated with alamethicin (60 μg/mg of protein) and incubated with various concentrations of raloxifene (10–200 μM). Incubations were carried out at 37°C for 5 min (human liver and intestinal microsomes) or 10 min (expressed UGT). Apparent K_m and V_max values were determined from linear regression analysis of Eadie-Hofstee plots to assess the potential for atypical versus typical Michaelis-Menten kinetics (Obach et al., 2001).

↵2-a Kinetic parameters could not be determined due to limited substrate solubility. Rates of glucuronide formation for UGT1A1 at 200 μM were 0.94 nmol/min/mg for R-4-G and 1.85 nmol/min/mg for R-6-G.
↵2-b Not detected.
↵2-c Kinetic parameters obtained via extrapolation (seeResults).