TABLE 2.
Effect of buffer species, pH, and temperature on the kinetic parameters of TryS for Spd
The apparent Km values for Spd were determined at a fixed ATP and GSH concentration of 2.1 and 1 mm, respectively. The kinetic parameters, which are the means of at least two determinations ± S.E., were obtained as described under “Experimental Procedures.”
| Buffer conditions | Kmapp | kcatapp |
|---|---|---|
| (μm) | (s−1) | |
| HEPES, pH 8.0 (25 °C) | 92 ± 25 | 0.13 ± 0.01 |
| HEPES, pH 7.0 (25 °C) | 397 ± 72 | 0.15 ± 0.01 |
| HEPES, pH 7.0 + 10 mm phosphate (25 °C) | 431 ± 40 | 0.14 ± 0.01 |
| Phosphate, pH 7.0 (25 °C) | 545 ± 38 | 0.28 ± 0.01 |
| Phosphate, pH 7.0 (37 °C) | 766 ± 77 | 1.01 ± 0.05 |