Example for determination of Ki for receptor-inhibitor binding affinity If we have determined KD from the Scatchard plot to be 0.85 μM and if the present inhibition study is carried out in the presence of a constant concentration of the primary ligand at 1 μM, then the dose-effect relationship in Table 17 can be analyzed with CompuSyn to yield Dm = 5.5202 μM, m = 0.73226, and r = 0.9903. Thus, based on eq. 24, Ki = IC50/[1+ (A/KA)] = 5.5202 μM/[1+ (1/0.85)] = 2.5363 μM.
| Inhibitor Concentration | Primary Ligand Binding | Fractional Inhibition (fa) |
|---|---|---|
| dpm | ||
| 0 (control) | 10,000 | |
| 1 μM | 7500 | 0.25 |
| 3 μM | 6000 | 0.4 |
| 10 μM | 5000 | 0.5 |
| 30 μM | 2000 | 0.8 |
| 100 μM | 1000 | 0.9 |
| 300 μM | 500 | 0.95 |