TABLE 4

Kinetic parameters for SN-38 glucuronidation by human UGT1A9 allozymes

The values of apparent Km and Vmax for the formation of SN-38 glucuronide were determined using microsomal preparations from UGT1A9-HEK293 cells and concentrations of SN-38 ranging from 0.1 to 200 μM. Activities are normalized by the expressed UGT protein levels determined by Western blot. Values were expressed as the mean ± S.D. of at least three independent experiments performed in duplicate from Lineweaver-Burk plots.


UGT1A9 Allozymes

Apparent Km

Vmax

Catalytic Efficiencies Vmax/Km
μM pmol / min / mg protein μl / h / mg
UGT1A9*1 3.0 ± 0.5 316.3 ± 52.0 105
UGT1A9*2 5.1 ± 1.8 324.4 ± 95.1 63
UGT1A9*3
3.2 ± 0.9
11.9 ± 2.6*
4
  • * p < 0.002 compared with UGT1A9*1.