TABLE 5.
Characterizations of ectoine synthetic enzymes from H. elongata OUT30018
| Property | Value for enzyme:
|
||
|---|---|---|---|
| DABA aminotransferasea | DABA acetyltransferase | Ectoine synthase | |
| Optimum conditions for activity | |||
| pH | 8.6–8.7 | 8.2 | 8.5–9.0 |
| Temp (°C) | 25 | 20 | 0–10 (NaCl, 0.05 M) |
| 15 (NaCl, 0.77 M) | |||
| 30 (NaCl, 3.0 M) | |||
| Concn of NaCl (M) | 0.5b | 0.4 | 0.5 (15°C) |
| Kinetic constants | |||
| Km (mM) | 9.1 (l-Glu) | NDc | 11 (NaCl, 0.05 M) |
| 4.5 (dl-ASA) | 8.4 (NaCl, 0.77 M) | ||
| Vmax (μmol min−1 mg−1) | 12 (dl-ASA) | ND | 85 (NaCl, 0.05 M) |
| 56 (NaCl, 0.77 M) | |||
a
Forward reaction.
b
Although activities of both forward and reverse directions decreased with increasing concentrations of NaCl, the decrease in the activity for the reverse reaction occurred more rapidly than that for the forward reaction up to 1 M NaCl. The optimal concentration of NaCl for the forward reaction was determined as the concentration at which the ratio of the activity for the forward reaction to that for the reverse reaction was maximum.
c
ND, not determined.