Table 2.
Kinetic parameters of racemases determined on select d- and l-amino acidsa
| Enzyme | Substrate |
Km (mM) |
kcat (s−1) |
kcat
Km−1 (M−1 s−1) |
|||
|---|---|---|---|---|---|---|---|
| d → l | l → d | d → l | l → d | d → l | l → d | ||
| Alanine racemase Alr | Lys | 0.36 ± 0.06 | 8.96 ± 1.52 | 274.5 ± 6.7 | 1,681.7 ± 161.7 | 7.63 × 105 | 1.88 × 105 |
| Ala | 15.71 ± 2.79 | 12.62 ± 0.74 | 8.83 ± 0.00 | 7.33 ± 0.00 | 5.62 × 102 | 5.81 × 102 | |
| Alanine racemase DadX | Ala | 7.73 ± 0.63 | 24.57 ± 2.64 | 37.47 ± 2.67 | 92.0 ± 11.6 | 4.85 × 103 | 3.74 × 103 |
| Proline racemase | HyPro (cis-d- and trans-l-) | 5.26 ± 1.12 | 15.04 ± 4.19 | 69.63 ± 8.60 | 7.74 ± 0.00 | 1.32 × 104 | 5.15 × 102 |
a
The substrates with the highest normalized percent activity were chosen for kinetic analysis, as were d-/l-Ala for Alr and trans-l-HyPro for proline racemase. Vmax and Km values were determined via nonlinear regression according to the Michaelis-Menten equation. kcat values were calculated by dividing Vmax by the enzyme concentration.