Enzyme kinetic parameters for the glucuronidation of estriol, 16-epiestriol, and 17-epiestriol by UGTs 1A10 and 2B7 as well as the mutant 1A10-F93G
Formation of the three glucuronides (g) from the different substrates was assayed in the cases of UGT1A10 and the mutant 1A10-F93G, whereas formation of 16-glucuronide by UGT2B7 was assayed when the substrate was estriol or 16-epiestriol; formation of 17-glucuronide by UGT2B7 was assayed when the substrate was 17-epiestriol.
| UGT1A10 (3-g) | 1A10-F93G (3-g) | UGT2B7 (16-g or 17-g) | |
|---|---|---|---|
| Estriol | (16-g) | ||
| Vmax (pmol/min/mg) | 1200 ± 28.1 | 7535 ± 618 | 1509 ± 27.7 |
| Km (µM) | 68.4 ± 4.7 | 230 ± 29.7 | 10.3 ± 0.8 |
| 16-epiestriol | (16-g) | ||
| Vmax (pmol/min/mg) | 7700 ± 740 | 2249 ± 201 | 3866 ± 788 |
| Km (µM) | 59.8 ± 8.0 | 186 ± 28.0 | 38.4 ± 11.4 |
| Ki (µM)a | 98.1 ± 16.6 | 162 ± 86.4 | |
| 17-epiestriol | (17-g) | ||
| Vmax (pmol/min/mg) | 958 ± 75.0 | 5712 ± 216 | 820 ± 18.3 |
| Km (µM) | 337 ± 42.1 | 51.1 ± 5.4 | 0.6 ± 0.1 |
UGTs, UDP-glucuronosyltransferases.
↵a Ki values are indicated when the kinetic curves fit best to the Michaelis-Menten with substrate inhibition model.