Kinetic Parameters for PC Activation by Thrombin and fXa on PC/PS/PE Vesicles in the Presence of Heparin or Dextran Sulfate
| . | Km (μmol/L) . | kcat (mol/min/ mol) . | kcat/ Km . |
|---|---|---|---|
| Thrombin (heparin) | 2.3 ± 0.4 | 0.36 ± 0.02 | 0.16 |
| Thrombin (dextran sulfate) | 0.7 ± 0.1 | 0.82 ± 0.05 | 1.17 |
| fXa (heparin) | 0.55 ± 0.04 | 0.17 ± 0.01 | 0.31 |
| fXa (dextran sulfate) | 0.15 ± 0.04 | 0.65 ± 0.19 | 4.33 |
| . | Km (μmol/L) . | kcat (mol/min/ mol) . | kcat/ Km . |
|---|---|---|---|
| Thrombin (heparin) | 2.3 ± 0.4 | 0.36 ± 0.02 | 0.16 |
| Thrombin (dextran sulfate) | 0.7 ± 0.1 | 0.82 ± 0.05 | 1.17 |
| fXa (heparin) | 0.55 ± 0.04 | 0.17 ± 0.01 | 0.31 |
| fXa (dextran sulfate) | 0.15 ± 0.04 | 0.65 ± 0.19 | 4.33 |
The kinetic constants were determined by incubating PC (0.1 to 12.5 μmol/L) with 5 nmol/L thrombin or fXa in the absence or presence of 100 μg/mL PC/PS/PE vesicles in TBS buffer containing 1 mg/mL BSA, 0.1% PEG 8000, and 5 mmol/L Ca2+ and 25 μg/mL heparin or dextran sulfate at room temperature. The kinetic values were determined from the rate of APC generated in each reaction as described under the Materials and Methods.