TABLE 2

Kinetic models and constants for 4MU glucuronidation by human UGT isoforms

Isoform
Empirical Modelsa,b,c
Two-Site Model
Km or S50
 Ksi
 Vmax
 Ks
 Vmax
 α, βd
μM pmol/min · mg protein μM pmol/min · mg protein
1A1a 113 ± 3 308 ± 16
1A3b 1159 ± 75 741 ± 55 1265 ± 51 1329 ± 72 1408 ± 60 α = 0.28 ± 0.04; β = 0.11 ± 0.03
1A4 N.D.
1A6a 109 ± 3.7 143,897 ± 1713
1A7a 14 ± 1.2 36,037 ± 810
1A8b 730 ± 67 1263 ± 146 9213 ± 603 750 ± 63 9277 ± 534 α = 0.77 ± 0.18; β = 0.21 ± 0.04
1A9b 8.0 ± 0.6 226 ± 53 9016 ± 364 8.2 ± 2.9 7198 ± 288 β = 0.9 ± 0.5f
1A10a 31 ± 2 13,688 ± 300
2B7c e 335 ± 8 168 ± 5 1914 ± 336 176 ± 5 α = 0.03 ± 0.01g
2B15b 253 ± 46 1744 ± 384 26 ± 2 463 ± 73 37 ± 4 β = 0.16 ± 0.07f
2B17b
4204 ± 559
326 ± 48
50 ± 6

  • N.D., not determined.

  • ↵ a Michaelis-Menten; b Substrate inhibition; c Hill equation.

  • ↵ d Interaction factors from two-site model.

  • ↵ e n = 1.9 ± 0.1 from Hill equation.

  • ↵ f α 0.9-1; g β = 2.