TABLE 2

The enzyme kinetic parameters for eight UGT1A isoenzymes with appropriate aglycone substrates

The initial rate data were fitted to eq. 2 omitting the high substrate concentrations with obvious substrate inhibition.


Enzyme

Vmax

Km (UDPGA)

KAX (UDPGA)

Km (Substrate)

Substrate
pmol min-1 mg-1 μM
UGT1A1 920 ± 35 409 ± 40 1402 ± 235 12.2 ± 1.77 Ethinylestradiol
UGT1A3 6946 ± 149 371 ± 22.3 699 ± 25.7 500 ± 17.7 Scopoletin
UGT1A4 5.89 ± 0.065 201 ± 6.20 342 ± 25.9 16.6 ± 0.738 1-Hydroxypyrene
UGT1A6 1261 ± 24.3 51.5 ± 3.26 163 ± 8.87 3.36 ± 0.134 1-Naphthol
5386 ± 72.0 166 ± 6.63 252 ± 13.2 194 ± 6.42 Scopoletin
UGT1A7 13,821 ± 72.6 248 ± 3.17 316 ± 8.54 23.0 ± 0.355 Entacapone
UGT1A8 2554 ± 87.3 1256 ± 75.5 1264 ± 130 20.7 ± 1.79 4-Hydroxyestrone
2344 ± 84.6 875 ± 70.6 1159 ± 111 63.3 ± 4.97 Entacapone
UGT1A9 10,171 ± 51.9 388 ± 5.26 186 ± 6.90 20.7 ± 0.266 Entacapone
1849 ± 44.1 87.9 ± 5.97 111 ± 11.2 36.7 ± 2.09 Scopoletin
UGT1A10
4716 ± 70.5
670 ± 23.1
693 ± 48.7
28.9 ± 1.20
Entacapone