UGT Isoform | 7-O-Glucuronidation | 3′-O-Glucuronidation | ||||
---|---|---|---|---|---|---|
Km | Vmax | Vmax/Km | Km | Vmax | Vmax/Km | |
μM | nmol min−1 mg protein−1 | μl min−1 mg protein−1 | μM | nmol min−1 mg protein−1 | μl min−1 mg protein−1 | |
UGT1A1 | 4.0 ± 1.3 | 1.35 ± 0.29 | 339 | 1.2 ± 0.5 | 0.46 ± 0.06 | 376 |
UGT1A3 | 16.5 ± 4.6 | 3.94 ± 0.74 | 239 | N.D. | N.D. | |
UGT1A4 | N.D.a | N.D.a | —a | N.D. | N.D. | |
UGT1A6 | —b | —b | 18b | N.D. | N.D. | |
UGT1A7 | 105 ± 67.9 | 0.47 ± 0.04 | 5 | 8.7 ± 1.6 | 2.47 ± 0.63 | 285 |
UGT1A8 | 63.3 ± 11.8 | 2.33 ± 1.20 | 37 | 19.2 ± 3.9 | 3.18 ± 1.78 | 166 |
UGT1A9 | 5.3 ± 0.8 | 2.19 ± 0.10 | 411 | 4.0 ± 0.3 | 3.89 ± 0.20 | 981 |
UGT1A10 | 30.4 ± 8.2 | 2.82 ± 0.69 | 93 | 31.2 ± 12.6 | 0.89 ± 0.29 | 28 |
UGT2B4 | 119 ± 43.7 | 0.42 ± 0.09 | 4 | N.D. | N.D. | |
UGT2B7 | 53.9 ± 17.6 | 1.53 ± 0.25 | 28 | 42.4 ± 13.9 | 0.88 ± 0.23 | 21 |
UGT2B15 | 34.5 ± 1.6 | 0.28 ± 0.01 | 8 | 29.9 ± 0.3 | 1.19 ± 0.02 | 40 |
UGT2B17 | N.D.c | N.D.c | —c | N.D.c | N.D.c | —c |
N.D., not detectable.
↵a UGT1A4 very poorly glucuronidated hesperetin into solely hesperetin 7-O-glucuronide, only measurable at the highest test concentration (50 μM), precluding determination of kinetics.
↵b Conjugation velocity by UGT1A6 of hesperetin into hesperetin 7-O-glucuronide occurred in a linear manner with dose (0.018 nmol min−1 mg of protein−1 μmol of hesperetin−1), precluding determination of the individual Michaelis-Menten parameters Vmax and Km, but allowing the definition of the catalytic efficiency because the slope of the linear relationship between the rate of formation as a function of the substrate concentration equals Vmax/Km.
↵c UGT2B17 very poorly glucuronidated hesperetin, only measurable at the highest test concentrations (50 μM).