Table 2.
Enzyme kinetic parameters for the formation of verproside glucuronides, M1 and M2, from verproside in human liver microsomes, intestinal microsomes, and cDNA-expressed UDP-glucuronosyltransferase (UGT)1A1, UGT1A8, UGT1A9, and UGT1A10 supersomes.
| Enzymes | M1 Formation | M2 Formation | ||||||
|---|---|---|---|---|---|---|---|---|
| Km (μM) | Vmax | n | Clint | Km (μM) | Vmax | n | Clint | |
| Human Liver Microsomes | 791.3 (174.9) | 22.6 (2.5) | 1.2 | 0.029 | 1109.9 (265.9) | 20.0 (2.5) | 1.1 | 0.018 |
| Human Intestinal Microsomes | 1251.8 (1608.4) | 159.4 (100.3) | 1.1 | 0.126 | 1215.2 (1460.9) | 810.2 (449.0) | 1.0 | 0.667 |
| UGT1A1 | 316.5 (54.2) | 32.4 (2.6) | 1.4 | 0.102 | 363.7 (53.1) | 16.3 (1.2) | 1.5 | 0.045 |
| UGT1A8 | 492.3 (30.1) | 77.4 (1.9) | 1.1 | 0.157 | 1158.7 (159.4) | 34.2 (2.0) | 0.9 | 0.030 |
| UGT1A9 | 2272.1 (2873.8) | 43.2 (31.4) | 1.1 | 0.019 | 1052.5 (440.9) | 33.0 (6.8) | 1.1 | 0.031 |
| UGT1A10 | 802.3 (266.4) | 280.5 (54.6) | 1.4 | 0.350 | 894.1 (229.5) | 50.9 (6.4) | 1.1 | 0.057 |
Vmax: pmol/min/mg protein, Clint (Vmax/Km): μL/min/mg protein, n: Hill coefficient. Standard errors are presented in parentheses. The amounts of the verproside glucuronides, M1 and M2, were determined using the calibration curve for verproside.