TABLE 2. Effect of SC-(1–325) binding to ProT and α-thrombin on the hydrolysis of tripeptide-pNA substrates.
Michaelis-Menten kinetic parameters determined for the indicated enzyme species and substrates are listed. The parameters were obtained by nonlinear least squares fitting of the Michaelis-Menten equation to the initial rates or fitting of the integrated equation to progress curves for tight binding substrates in the presence of saturating concentrations of SC-(1–325). The experiments were performed and analyzed as described under “Experimental Procedures.”
| Substrate | Enzyme | kcat | Km | Ki | kcat/Km |
|---|---|---|---|---|---|
| s−1 | μM | μM | μM−1 s−1 ×103 | ||
| D-Phe-Pip-Arg-pNA | α-Thrombin | 77 ± 1 | 2.5 ± 0.2 | 11.5 ± 0.2 | 31,000 ± 1,500 |
| SC-(1–325)·thrombin | 58.1 ± 0.3 | 2.0 ± 0.1 | 9 ± 1 | 29,000 ± 1,000 | |
| SC-(1–325)·ProT | 72.2 ± 0.1 | 1.2 ± 0.1 | 6.2 ± 0.1 | 58,000 ± 300 | |
| D-Ile-Pro-Arg-pNA | α-Thrombin | 52 ± 1.0 | 2.0 ± 0.1 | 100 ± 70 | 26,000 ± 1,000 |
| SC-(1–325)·thrombin | 25.6 ± 0.3 | 1.0 ± 0.1 | 2.5 ± 0.4 | 25,000 ± 1,000 | |
| SC-(1–325)·ProT | 36 ± 1.0 | 2.2 ± 0.4 | 100 ± 180 | 16,000 ± 2,000 | |
| D-Phe-Pro-Arg-pNA | α-Thrombin | 13.8 ± 0.1 | 0.6 ± 0.1 | 6.1 ± 0.3 | 24,700 ± 800 |
| SC-(1–325)·thrombin | 5.6 ± 0.1 | 1.0 ± 0.1 | 5.2 ± 0.6 | 5,100 ± 400 | |
| SC-(1–325)·ProT | 12.5 ± 0.2 | 2.0 ± 0.2 | 3.8 ± 0.5 | 6,400 ± 400 | |
| CH3-Gly-Gly-Arg-pNA | α-Thrombin | 13 ± 1 | 190 ± 30 | 70 ± 10 | |
| SC-(1–325)·thrombin | 17 ± 1 | 150 ± 30 | 110 ± 30 | ||
| SC-(1–325)·ProT | 6.1 ± 0.2 | 126 ± 10 | 48 ± 5 | ||
| Ser-Ala-Arg-pNA | α-Thrombin | 60 ± 10 | 980 ± 360 | 60 ± 20 | |
| SC-(1–325)·thrombin | 120 ± 10 | 750 ± 130 | 160 ± 30 | ||
| SC-(1–325)·ProT | 63 ± 5 | 2100 ± 300 | 30 ± 20 | ||
| Gly-Val-Arg-pNA | α-Thrombin | 146 ± 4 | 1660 ± 70 | 88 ± 5 | |
| SC-(1–325)·thrombin | 330 ± 10 | 840 ± 60 | 390 ± 40 | ||
| SC-(1–325)·ProT | 62 ± 3 | 900 ± 100 | 69 ± 8 |