Table 5. Kinetic parameters of seven bacterial IMPDHs, with NAD as variable substrate.
Reaction rates were determined at a constant saturating concentration of IMP (1 mM for IMPDHbt and IMPDHkp; 2 mM for IMPDHba, IMPDHsa and IMPDHlpp; 3 mM for IMPDHnm; 7 mM for IMPDHpa) and in the absence or presence of MgATP (2 mM for IMPDHnm; 3 mM for IMPDHpa; 5 mM for IMPDHlpp), and fitted according to the Michaelis-Menten equation (see under Materials and Methods).
| Enzyme | Without MgATP | With MgATP | |||||
|---|---|---|---|---|---|---|---|
| Vm (U/mg) | Km (μM) | Ki | Vm (U/mg) | Km (μM) | Ki (μM) | ||
| Class I | IMPDHlpp | 1.88 ± 0.06 | 998 ± 96 | - | 4.06 ± 0.19 | 1762 ± 281 | - |
| IMPDHnm | 1.62 ± 0.03 | 269 ± 22 | - | 3.48 ± 0.07 | 477 ± 29 | - | |
| IMPDHpa* | 2.26 ± 0.07 | 139 ± 14 | - | 9.00 ± 0.5 | 498 ± 44 | 4067 ± 550 | |
| Class II | IMPDHbt | 2.82 ± 0.07 | 355 ± 27 | 2.78 ± 0.14 | 418 ± 60 | - | |
| IMPDHba | 6.53 ± 0.19 | 2209 ± 232 | - | 5.93 ± 0.36 | 1994 ± 264 | - | |
| IMPDHkp | 14.00 ± 0.10 | 1175 ± 103 | - | 13.80 ± 0.30 | 1122 ± 65 | - | |
| IMPDHsa | 11.10 ± 0.12 | 2350 ± 215 | - | 11.80 ± 0.50 | 1762 ± 230 | - | |
*Values for IMPDHpa were taken from Labesse et al. [16].
ND: not determined.