Table 1.
Steady-state kinetic analysis of AtPMT isoforms
Enzyme assays were performed using purified protein as described under “Experimental procedures.” Kinetic parameters for each phosphobase substrate were determined at 2 mm SAM. Kinetic parameters for SAM were determined at 3 mm pEA and at 10 mm pDME. Values shown are the mean ± S.D. for n = 3.
| Substrate | Parameter | AtPMT1 | AtPMT2 | AtPMT3 |
|---|---|---|---|---|
| pEA | kcat (min−1) | 12.3 ± 0.6 | 16.1 ± 2.5 | 5.2 ± 1.0 |
| Km (μm) | 156 ± 24 | 408 ± 143 | 284 ± 96 | |
| kcat/Km (m−1 s−1) | 1,314 | 658 | 305 | |
| pMME | kcat (min−1) | 8.2 ± 0.4 | 12.7 ± 0.6 | 2.5 ± 0.3 |
| Km (μm) | 278 ± 38 | 577 ± 72 | 201 ± 59 | |
| kcat/Km (m−1 s−1) | 489 | 367 | 209 | |
| pDME | kcat (min−1) | 13.1 ± 1.4 | 16.0 ± 1.0 | 2.4 ± 0.2 |
| Km (μm) | 507 ± 115 | 653 ± 98 | 249 ± 69 | |
| kcat/Km (m−1 s−1) | 433 | 408 | 161 | |
| SAM (pEA) | kcat (min−1) | 7.8 ± 0.4 | 16.0 ± 0.7 | 3.7 ± 0.2 |
| Km (μm) | 89.7 ± 11.8 | 308 ± 33 | 69.1 ± 9.6 | |
| kcat/Km (m−1 s−1) | 1,453 | 866 | 897 | |
| SAM (pDME) | kcat (min−1) | 9.9 ± 0.9 | 12.8 ± 0.3 | 1.5 ± 0.1 |
| Km (μm) | 215 ± 41 | 212 ± 13 | 92.8 ± 7.5 | |
| kcat/Km (m−1 s−1) | 767 | 1,006 | 266 |