TABLE 1

Kinetic analysis of UGT3A2 activity against PAH substrates using alternative sugars as cosubstrates^{^a}

Substrate	UDP-Glucose			UDP-Xylose			UDP-Xyl/UDP-Glc
Substrate	K_m	V_max	V_max/K_m	K_m	V_max	V_max/K_m	K_m Ratio	V_max/K_m Ratio
	μM	pmol·min^−l·mg⁻¹	μl·min⁻¹·mg⁻¹	μM	pmol·min^−l·mg⁻¹	μl·min⁻¹·mg⁻¹
1-Naphthol	225 ± 31	489 ± 24	2.2 ± 0.40	129 ± 32^*	453 ± 58	3.5 ± 0.28^*	0.57	1.6
1-OH-pyrene	3.3 ± 0.18	1305 ± 118	396 ± 52	1.2 ± 0.19^*	998 ± 204	840 ± 254	0.36	2.1
1-OH-benzo(a)pyrene	11 ± 2.4	2035 ± 333	202 ± 54	6.1 ± 1.5	1135 ± 117^*	199 ± 53	0.55	0.98
3-OH-benzo(a)pyrene	7.5 ± 0.93	1734 ± 181	238 ± 51	7.2 ± 2.9	2525 ± 599	389 ± 98	0.96	1.6
7-OH-benzo(a)pyrene	7.8 ± 1.9	430 ± 67	56 ± 6.2	8.5 ± 0.53	683 ± 227	80 ± 26	1.1	1.4
9-OH-benzo(a)pyrene	12 ± 0.55	984 ± 85	84 ± 4.7	9.6 ± 0.87^*	1227 ± 107	129 ± 10^*	0.80	1.5
Benzo(a)pyrene-7,8-diol	397 ± 67	13 ± 0.51	0.034 ± 0.0059	168 ± 30^*	18 ± 1.2^*	0.11 ± 0.011^*	0.42	3.2
Benzo(a)pyrene-9,10-diol	190 ± 16	1.6 ± 0.039	0.0087 ± 0.00069	120 ± 36	4.3 ± 0.57^*	0.038 ± 0.010^*	0.63	4.4
Dibenzo(a,l)pyrene-11,12-diol	96 ± 8.3	7.1 ± 0.44	0.074 ± 0.0058	143 ± 6.8^*	7.3 ± 0.33	0.051 ± 0.0015^*	1.5	0.69
5-Methylchrysene-1,2-diol	1250 ± 319	37 ± 4.8	0.031 ± 0.0047	124 ± 6.8^*	2.5 ± 0.72^*	0.020 ± 0.0041	0.099	0.65

↵^a Data are expressed as milligrams of total microsomal protein. The K_m, V_max, and V_max/K_m values represent the mean ± S.D. of three independent experiments.
↵* P < 0.05 vs. corresponding value for UGT3A2-overexpressing microsomes using UDP-Glc as the cosubstrate.