Vmax and Km values determined from three independent curves and the catalytic efficiencies (Vmax/Km) derived from these values for the sulfonation of hesperetin (1 up to 50 μM unless stated otherwise) by individual SULT enzymes
Data are means ± S.E.M.
| SULT Isoform | 7-O-Sulfonation | 3′-O-Sulfonation | ||||
|---|---|---|---|---|---|---|
| Km | Vmax | Vmax/Km | Km | Vmax | Vmax/Km | |
| μM | nmol min−1 mg protein−1 | μl min−1 mg protein−1 | μM | nmol min−1 mg protein−1 | μl min−1 mg protein−1 | |
| SULT1A1 | N.D. | N.D. | <0.15a | —a | —a | |
| SULT1A2 | N.D. | N.D. | 0.5 ± 0.2b | 454 ± 94.8b | 881,553b | |
| SULT1A3 | 12.5 ± 3.3 | 89.9 ± 7.43 | 7178 | 13.2 ± 3.0 | 276 ± 24.8 | 20,964 |
| SULT1B1 | 3.9 ± 0.5 | 3.54 ± 0.66 | 899 | 4.3 ± 0.2 | 21.5 ± 2.14 | 5003 |
| SULT1C2 | 66.7 ± 16.1 | 18.8 ± 6.83 | 282 | 28.3 ± 14.5 | 1.45 ± 0.46 | 51 |
| SULT1C3 | N.D. | N.D. | N.D. | N.D. | ||
| SULT1C4 | 0.1 ± 0.0c | 87.4 ± 8.13c | 1,117,263c | N.D. | N.D. | |
| SULT1E1 | N.D. | N.D. | 2.5 ± 1.0d | 538 ± 134d | 219,242d | |
| SULT2A1 | 80.2 ± 21.0 | 10.2 ± 1.96 | 127 | N.D. | N.D. | |
| SULT2B1_v1 | N.D. | N.D. | N.D. | N.D. | ||
| SULT2B1_v2 | N.D. | N.D. | N.D. | N.D. | ||
| SULT4A1_v2 | N.D. | N.D. | N.D. | N.D. | ||
N.D., not detectable.
↵a SULT1A1 demonstrated strong substrate inhibition at concentrations >0.1 μM, precluding determination of kinetic parameters.
↵b SULT1A2 showed substrate inhibition at concentrations >1 μM hesperetin; Ki = 1.9 μM.
↵c SULT1C4 showed substrate inhibition at concentrations >1 μM hesperetin; Ki = 23.5 μM.
↵d SULT1E1 showed substrate inhibition at concentrations >3 μM hesperetin; Ki = 12.9 μM.