Table 1. Inhibition of MASP-2 by SFMI2 and Its Terminally Capped and Thioether-Linked Derivatives.
| variant | KI* (μM) | KI (μM) |
|---|---|---|
| SFMI2 | 0.30 ± 0.01 | 0.21 |
| Ac-SFMI2 | 0.20 ± 0.01 | 0.14 |
| SFMI2-NH2 | 0.17 ± 0.00 | 0.12 |
| SFMI2cap | 0.10 ± 0.01 | 0.07 |
| SFMI2cap-Dap fraction 1a | 0.69 ± 0.05 | 0.49 |
| SFMI2cap-Dap fraction 2a | 6.35 ± 0.44 | 4.52 |
| SFMI2cap-Dab | 57 ± 2 | 41 |
| SFMI2cap-Orn | 84 ± 19 | 60 |
| SFMI2cap-Lys | 58 ± 1 | 41 |
| SFMI2cap-Agl | 827 ± 129 | 589 |
a
For SFMI2cap-Dap, two isomers could be isolated (see Supporting Information Results, Characterization of SFMI2 and derived peptides by HPLC-MS). KI* stands for apparent inhibitory constant values with standard error of measurement (SEM) values indicated. The KI values are called apparent because they are biased by the substrate competing with the inhibitor for enzyme binding. The genuine KI is calculated as follows: KI = KI*/(1 + 1/KM), where KM is the Michaelis constant. Details of experimental procedures are provided in the Supporting Information.