TABLE 1.
Kinetic parameters for selected substratesa
| AspAT | Substrate | Cosubstrate | Apparent Vmax (μmol/min/mg) | Apparent Km (mM) |
|---|---|---|---|---|
| C. fasciculata cytoplasmic | Asp | KG | 3.37 ± 0.31 | 5.00 ± 0.98 |
| Tyr | KG | 3.30 ± 0.08 | 4.77 ± 0.20 | |
| Gln | KG | 23.82 ± 2.52 | 32.02 ± 4.23 | |
| Ala | KG | 2.76 ± 0.14 | 3.10 ± 0.38 | |
| KG | Tyr | 3.30 ± 0.11 | 6.78 ± 0.41 | |
| KMTB | Glu | 1.87 ± 0.13 | 6.95 ± 0.89 | |
| Glu | KMTB | 2.27 ± 0.06 | 11.34 ± 0.50 | |
| Tyr | KMTB | 1.97 ± 0.24 | 10.12 ± 1.72 | |
| Phe | KMTB | 2.50 ± 0.08 | 25.99 ± 1.13 | |
| Trp | KMTB | 2.54 ± 0.09 | 11.94 ± 0.69 | |
| His | KMTB | 4.00 ± 0.65 | 16.38 ± 3.90 | |
| Leu | KMTB | 2.97 ± 0.03 | 12.77 ± 0.20 | |
| T. brucei brucei cytoplasmic | Asp | KG | 4.59 ± 0.33 | 10.38 ± 1.22 |
| Tyr | KG | 8.68 ± 1.24 | 17.10 ± 3.04 | |
| Gln | KG | 16.68 ± 1.53 | 21.47 ± 2.67 | |
| Ala | KG | 3.50 ± 0.26 | 7.83 ± 0.88 | |
| KG | Tyr | 2.83 ± 0.16 | 6.96 ± 0.75 | |
| KMTB | Glu | 2.05 ± 0.13 | 8.69 ± 0.24 | |
| Glu | KMTB | 1.97 ± 0.11 | 8.93 ± 0.84 | |
| Tyr | KMTB | 1.47 ± 0.21 | 7.25 ± 1.53 | |
| Phe | KMTB | 1.69 ± 0.08 | 16.12 ± 1.07 | |
| Trp | KMTB | 1.63 ± 0.16 | 6.85 ± 1.29 | |
| His | KMTB | 4.63 ± 0.37 | 19.53 ± 2.20 | |
| Leu | KMTB | 2.09 ± 0.06 | 8.76 ± 0.47 | |
| T. brucei brucei mitochondrial | Asp | KG | 8.40 ± 0.44 | 9.80 ± 0.87 |
| Tyr | KG | 3.14 ± 0.27 | 1.94 ± 0.39 | |
| Gln | KG | 0 | ||
| Ala | KG | 0 | ||
| KG | Tyr | 2.88 ± 0.88 | 2.13 ± 0.17 | |
| KMTB | Glu | 2.62 ± 0.07 | 4.23 ± 0.26 | |
| Glu | KMTB | 4.43 ± 0.25 | 10.39 ± 0.96 | |
| Tyr | KMTB | 0.42 ± 0.02 | 0.79 ± 0.09 | |
| Phe | KMTB | 0.92 ± 0.06 | 4.28 ± 0.65 | |
| Trp | KMTB | 0.31 ± 0.01 | 0.44 ± 0.08 | |
| His | KMTB | 4.62 ± 1.17 | 27.42 ± 8.97 | |
| Leu | KMTB | 0.06 ± 0.01 | 0.38 ± 0.26 | |
| G. intestinalis cytoplasmic | Asp | KG | 7.29 ± 1.39 | 11.30 ± 3.47 |
| Tyr | KG | 5.88 ± 0.62 | 6.90 ± 1.13 | |
| Gln | KG | 0 | ||
| Ala | KG | 0 | ||
| KG | Tyr | 3.75 ± 0.24 | 5.44 ± 0.72 | |
| KMTB | Glu | 3.67 ± 0.19 | 10.64 ± 0.92 | |
| Glu | KMTB | 3.63 ± 0.18 | 10.94 ± 0.91 | |
| Tyr | KMTB | 1.84 ± 0.15 | 5.61 ± 0.72 | |
| Phe | KMTB | 3.34 ± 0.15 | 23.95 ± 1.41 | |
| Trp | KMTB | 4.85 ± 0.32 | 16.09 ± 1.54 | |
| His | KMTB | 6.60 ± 0.41 | 17.47 ± 1.54 | |
| Leu | KMTB | 2.88 ± 0.13 | 8.11 ± 0.64 | |
| P. falciparum | Asp | KG | 3.69 ± 0.41 | 5.48 ± 1.24 |
| Tyr | KG | 1.35 ± 0.08 | 1.47 ± 0.23 | |
| Gln | KG | 0 | ||
| Ala | KG | 0 | ||
| KG | Tyr | 1.03 ± 0.04 | 1.26 ± 0.15 | |
| KMTB | Glu | 0.45 ± 0.03 | 1.06 ± 0.28 | |
| Glu | KMTB | 0.96 ± 0.06 | 8.90 ± 1.00 | |
| Tyr | KMTB | 0.14 ± 0.01 | 0.44 ± 0.13 | |
| Phe | KMTB | 0.16 ± 0.01 | 0.79 ± 0.10 | |
| Trp | KMTB | 0.12 ± 0.01 | 0.72 ± 0.06 | |
| His | KMTB | 1.06 ± 0.16 | 16.34 ± 3.69 | |
| Leu | KMTB | 0.02 ± 0.01 | 0.77 ± 0.28 |
a
The recombinant enzymes were incubated with 10 mM cosubstrate (5 mM in the case of Tyr) and various amounts of substrate as outlined in Materials and Methods. Met production was quantified by HPLC, and kinetic constants were determined using nonlinear least-squares fitting to the Michaelis-Menten equation. Vmax and Km values are reported as the mean and standard deviation.