TABLE 4

Kinetic parameters for HFC glucuronidation by expressed UGTs and inhibition by silybin Expressed UGTs were pretreated with alamethacin (50 μg/mg protein) and incubated with varying concentrations of HFC to determine kinetic parameters as described under Materials and Methods. The data were fitted to either Michaelis-Menten (Km) or Hill kinetics (S50). IC50 values for inhibition of HFC glucuronidation by silybin were determined at the Km concentrations for each UGT isozyme. The enzyme rates shown represent the mean and standard deviation from three separate experiments.


Expressed UGT

Km/S50

Vmax

n

IC50
μM pmol/mg/min μM
UGT1A1 27 ± 5 860 ± 35 1.5 ± 0.2 1.4 ± 0.3
UGT1A6 47 ± 2 9333 ± 166 28 ± 3
UGT1A9 3.4 ± 1.1 4537 ± 265 1.9 ± 0.7 20 ± 3
UGT2B7 124 ± 19 2366 ± 180 92 ± 35
UGT2B15
16 ± 3
1786 ± 145
1.2 ± 0.2
75 ± 3