Table 1. Comparison of Steady State Kinetic Parameters at pH 7.0 for Numerous R67 DHFR Constructs.
| enzyme | kcat (s–1) | NADPH Km (μM) | DHF Km (μM) | kcat/Km(NADPH) (s–1 M–1) | kcat/Km(DHF) (s–1 M–1) | any DHF inhibition? |
|---|---|---|---|---|---|---|
| Quad3a | 0.81 ± 0.02 | 4.4 ± 0.4 | 6.7 ± 0.4 | 1.8 × 105 | 1.2 × 105 | no |
| K32R:1+3 | 0.41 ± 0.01 | 6.5 ± 0.6 | 3.9 ± 0.3 | 6.3 × 104 | 1.1 × 105 | no |
| K32R:1+3 plus Y69W:1+3 | 0.80 ± 0.03 | 3.8 ± 0.4 | 12 ± 1 | 2.1 × 105 | 6.7 × 104 | no |
| I68A:3 | 0.56 ± 0.02 | 3.5 ± 0.6 | 5.6 ± 0.6 | 1.6 × 105 | 1.0 × 105 | yes with a Kd2 of 8.6 ± 2.0 μM |
| wt R67 DHFRb | 1.3 ± 0.07 | 3.0 ± 0.06 | 5.8 ± 0.02 | 4.3 × 105 | 2.2 × 105 | no |