Table III.
Steady-state kinetic constants for hydrolysis of bioactive peptides by ECE-2
| Substrate |
Km
|
kcat
|
kcat/Km
|
|||
|---|---|---|---|---|---|---|
| ECE-2 | ECE-1a | ECE-2 | ECE-1a | ECE-2 | ECE-1a | |
| μM | s−1 | M−1s−1 | ||||
| Big ET-1 | 0.4 ± 0.03 | 2.0 ± 0.3 | 0.0002 ± 0.00002 | 0.052 ± 0.002 | 5.0 × 102 | 2.5 × 104 |
| Peptide E | 1.4 ± 0.17 | NAb | 0.004 ± 0.0002 | NA | 2.9 × 103 | NA |
| McaBk2 | 8.7 ± 0.7 | 6.0 ± 0.2 | 6.9 ± 0.4 | 110 ± 10 | 7.9 × 105 | 1.9 × 107 |
| Bradykinin | 27.4 ± 3.0 | 460.0 ± 10 | 5.8 ± 0.3 | 48 ± 2 | 2.1 × 105 | 1.0 × 105 |
| Dynorphin B | 48.4 ± 4.1 | NA | 8.8 ± 0.5 | NA | 1.8 × 105 | NA |
a
Data from Johnson and Ahn (31).
b
NA, not available.
In the case of Dyn B and peptide E where sequential cleavages of the substrate were observed upon prolonged incubation, the initial velocity measurements were performed under conditions where only the first cleavage occurred.