TABLE 3.
Kinetic constants for the hSULT1A1*1-catalyzed sulfation of 4-OHTAM, N-desTAM, and endoxifen
The sulfation of each metabolite was determined using 0.74 µg purified hSULT1A1*1. Data are the means ± S.E. from three independent experiments and were fit to either a standard uncompetitive substrate inhibition equation (for 4-OHTAM and endoxifen) or a Michaelis Menten equation (for N-desTAM). Calculation of kcat values was based on 68,312 as the dimeric molecular mass of hSULT1A1*1.
| Metabolite | Km | Vmax | kcat/Km | Ki |
|---|---|---|---|---|
| µM | nmol/min/mg | min−1µM−1 | µM | |
| 4-OHTAM | 26 ± 5 | 20 ± 3 | 0.050 ± 0.012 | 84 ± 19 |
| Endoxifen | 118 ± 82 | 35 ± 20 | 0.020 ± 0.018 | 26 ± 18 |
| N-desTAM | 44 ± 14 | 1.9 ± 0.2 | 0.003 ± 0.001 |