Table 2. Kinetic characterization of purified recombinant GS enzymes.
Km data for both β-alanine and glycine were assayed with a constant γ-EC concentration (1 mM). Km data for γ-glutamylcysteine were assayed with a β-alanine concentration of 10 mM for GmGS and a glycine concentration of 10 mM for all other enzymes. For Vmax, activities are expressed as pkat·(mg of pure protein)−1. Kcat/Km values presented in the Table are with respect to the acyl acceptor. ND, kinetic constants could not be determined due to the very low activities determined. Vmax values are given in pkat·(mg of purified GS)−1.
| Co-substrate | |||
|---|---|---|---|
| Kinetic constant | Glycine | β-Alanine | |
| GmGS | Vmax (pkat·mg−1) | 364±36 | 2132±152 |
| Km (mM) | 19±6 | 0.32±0.08 | |
| Kcat/Km (M−1·s−1) | 107 | 37083 | |
| Km for γ-EC (mM) | ND | 0.06±0.04 | |
| TaGS1 | Vmax (pkat·mg−1) | 663±35 | ND |
| Km (mM) | 0.16±0.04 | ND | |
| Kcat/Km (M−1·s−1) | 24003 | ND | |
| Km for γ-EC (mM) | 0.18±0.07 | ND | |
| TaGS2 | Vmax (pkat·mg−1) | 2817±172 | 5660±3153 |
| Km (mM) | 0.07±0.02 | 170±136 | |
| Kcat/Km (M−1·s−1) | 212404 | 175 | |
| Km for γ-EC (mM) | 0.10±0.02 | ND | |
| ZmGS | Vmax (pkat·mg−1) | 1304±179 | 372.4±597 |
| Km (mM) | 0.18±0.08 | 592±1077 | |
| Kcat/Km (M−1·s−1) | 38060 | 3.3 | |
| Km for γ-EC (mM) | 0.03±0.02 | ND | |