The bisubstrate enzyme kinetic parameters of 4-MU glucuronidation by UGT1A9
The data were interpreted by compulsory-order, ternary-complex mechanism based on steady-state assumption (eqs. 7 and 8). The values represent a best-fit result ± S.E. The calculated 95% CI are presented in the parenthesis. The reaction velocity is given per milligram of total protein in UGT1A9-enriched insect cell membranes. See Materials and Methods for additional details.
| Condition | Bisubstrate Enzyme Kinetics Parameters of 4-MU Glucuronidation by UGT1A9 | |||||
|---|---|---|---|---|---|---|
| Vmax | Km (4-MU) | Km (UDPGA) | Ki (UDPGA) | Ksi (4-MU) | Kinetic Model | |
| nmol · min−1 · mg−1 | μM | μM | μM | μM | r2 | |
| No BSA | 1.25 ± 0.04 (1.18–1.33) | 12.0 ± 1.1 (9.86–14.2) | 36.3 ± 8.7 (18.7–53.9) | 136 ± 26 (83.2–188) | Equation 7 (0.99) | |
| 0.1% BSA | 9.47 ± 0.13 (9.20–9.75) | 2.91 ± 0.16 (2.59–3.24) | 90.2 ± 8.6 (72.8–108) | 445 ± 46 (352–538) | Equation 7 (0.99) | |
| 0.1% BSA with substrate inhibition | 9.44 ± 0.19 (9.06–9.83) | 3.08 ± 0.22 (2.65–3.52) | 64.1 ± 5.4 (53.4–74.8) | 574 ± 60 (454–694) | 146 ± 8 (130–162) | Equation 8 (0.99) |
| 0.1% BSA reverse reaction | 0.872 ± 0.023 (0.826–0.918) | Km (4-MUG) 1339 ± 133 (1071–1607) | Km (UDP) 2.48 ± 0.66 (1.23–4.86) | Ki (UDP) 51.0 ± 9.7 (31.3–70.6) | Equation 7 (0.99) | |