TABLE 6.
Molecular, catalytic, and thermophilic properties of the proteins with CDase activity
| Parameter | Result for Amy1 | Result for Amy132 |
|---|---|---|
| Apparent molecular mass (kDa) | ||
| Native | 195a | 147 |
| Subunit | 85a | 68 |
| Calculated | 65.8 | 66 |
| Oligomeric structure | α2 | α2 |
| pH optimum | 6 | 5.5-6 |
| Temp optimum (°C) | 55 | 55 |
| Thermostability | ||
| Half-life at 55°C (min) | 30 | No loss of activity over 120 min |
| Half-life at 70°C (min) | 5 | 10 |
| Half-life at 55°C (min) at 1 mM DTE or 1M NaCl | 120 | No stabilization by DTE or NaCl |
| Substrate specificity (%)b | ||
| Starch | 69 | 14 |
| Amylose | 8 | 33 |
| Amylopectin | 82 | 0 |
| α-Cyclodextrin | 100 | 100 |
| β-Cyclodextrin | 69 | 80 |
| Pullulan | 0 | 15 |
| Glycogen | 1 | 0 |
| Maltotetraose | 3 | 1 |
| Maltoheptaose | 10 | 6 |
| Maltodextrin | 15 | 8 |
| Trehalose | 0 | 0 |
| Xylan (birch wood) | 0 | 0 |
| Kinetic constants (starch) | ||
| Vmax (U mg−1) | 47.5 | 150 |
| Km (g liter−1) | 6 | 63 |
| Vmax/Km | 7.9 | 2.3 |
| Kinetic constants (α-cyclodextrin) | ||
| Vmax (U mg−1) | 43 | 332 |
| Km (g liter−1) | 4 | 3.3 |
| Vmax/Km | 10.8 | 100 |
| Kinetic constants (β-cyclodextrin) | ||
| Vmax (U mg−1) | 34 | 200 |
| Km (g liter−1) | 8 | 2.4 |
| Vmax/Km | 4.3 | 83.3 |
a
With the N-terminal tag.
b
Determined with 0.5% (Amy132) and 1% (Amy1) substrate.