TABLE 5

Kinetic estimates for MPAG and AcMPAG formation by UGT1A8 and UGT2B7 variant allozymes

Kinetic parameter determination was performed by incubating MPA (25 to 1250 μM) with HEK293 cells stably expressing UGT1A8 and UGT2B7 variants. Velocity values were adjusted according to protein expression levels relative to the *1 allele determined by Western blot. All values are expressed as the mean ± S.E.M. of two to five experiments performed in duplicate.

Allozymes	MPAG					AcMPAG
Allozymes		K_m	Relative V_max	CL_int	K_m	Relative V_max	CL_int
UGT1A8	μM	pmol/min/mg	μl/min/mg	μM	pmol/min/mg	μl/min/mg
*1^a	411 ± 65	112,826 ± 5434	165	703 ± 144	532 ± 39	0.39
*2 (G¹⁷³)	296 ± 31	87,992 ± 4263	211	566 ± 9	242 ± 5**	0.22
*3 (Y²⁷⁷)	89 ± 11*	3296 ± 359 **	38	N.D.	N.D.	N.D.
*4 (V¹⁴⁴G¹⁷³)	105 ± 13*	30,470 ± 1102**	300	468 ± 40	120 ± 13*	0.26
*5 (G¹⁷³A²⁴⁰)	75 ± 10*	9273 ± 400**	132	278 ± 36	26 ± 5*	0.09
*6 (G¹²⁶)	333 ± 120	48,880 ± 8735*	164	483 ± 95	128 ± 20*	0.29
*7 (T²³¹)	288 ± 136	402 ± 1**	2	N.D.	N.D.	N.D.
*8 (L⁴³)	531 ± 18	40,451 ± 416*	50	1125 ± 226	164 ± 12*	0.11
*9 (N⁵³G¹⁷³)	683 ± 262	33,773 ± 3705*	39	672 ± 125	166 ± 8*	0.13
H⁵³N^b	441 ± 74	44,809 ± 1387*	63	773 ± 188	204 ± 23*	0.15
A¹⁴⁴V^b	130 ± 25*	66,479 ± 9498*	652	553 ± 43	403 ± 101	0.71
T²⁴⁰A^b	75 ± 18*	7261 ± 1386**	101	N.D.	N.D.	N.D.
UGT2B7
*1 (H²⁶⁸)	N.D.	N.D.	N.D.	183 ± 99	1993 ± 193	12
*2 (Y²⁶⁸)	N.D.	N.D.	N.D.	146 ± 61	2610 ± 805	18

Significant differences from the *1 allele; * p < 0.05, ** p < 0.001. N.D., not detectable.
↵ a UGT1A8*1 (S⁴³H⁵³S¹²⁶A¹⁴⁴A¹⁷³A²³¹T²⁴⁰C²⁷⁷).
↵ b Not encountered alone in the population studied.