Km values for sulfation of raloxifene and 4-OHT by human cytosolic SULTs
The SULTs were expressed in E. coli XL1-blue cells using the pKK233-2 vector and purified by DEAE-Sepharose chromatography. Km values were determined using substrate concentrations between 0.025 and 1 μM to avoid substrate inhibition. The PAPS concentration was 20 μM. Apparent Km values were calculated using the Enzyme Kinetics program (Trinity Software). The values represent means ± standard deviation of three separate determinations.
SULT | Km | ||
|---|---|---|---|
| Raloxifene | 4-OHT | ||
| μM | |||
| 1A1 | 1.8 ± 0.2 | 0.8 ± 0.1 | |
| 1A3 | 2.4 ± 0.4 | ||
| 1B1 | 1.8 ± 0.2 | ||
| 1C2 | 10.3 ± 1.1 | ||
| 1E1 | a | 0.2 ± 0.1 | |
| 2A1 | 0.3 ± 0.1 | 1.6 ± 0.3 | |
| 2B1a/b | 4.2 ± 0.5 |
| |
↵ a An apparent Km could not be reliably estimated for SULT1E1 due to the formation of multiple sulfated products for raloxifene.