Table 1.
Relative affinity and selectivity of IGF-I, IGF-II, and IGFBP ligand inhibitor (IGFBP-LI) for IGF-binding proteins and the type-I and type-II IGF receptors
| Protein or receptor | IGF-I | Ki, nM
|
|
|---|---|---|---|
| IGF-II | IGFBP-LI | ||
| IGFBP-1 | 0.12 ± 0.03 | 0.051 ± 0.008 | 1.91 ± 0.10 |
| IGFBP-2 | 0.06 ± 0.01 | 0.010 ± 0.005 | 1.92 ± 0.80 |
| IGFBP-3 | 0.21 ± 0.04 | 0.023 ± 0.005 | 1.80 ± 0.20 |
| IGFBP-4 | 0.10 ± 0.03 | 0.032 ± 0.004 | 0.28 ± 0.10 |
| IGFBP-5 | 0.22 ± 0.04 | 0.040 ± 0.004 | 3.91 ± 2.40 |
| Type-I receptor | 1.5 | 3.0 | >10,000 |
| Type-II receptor | 400 | 0.2 | >10,000 |
The relative affinities of hIGF-I, hIGF-II, and the IGFBP-LI, [Leu24,59,60, Ala31]hIGF-I for the various IGFBPs were determined in radioligand-binding assays as described in Materials and Methods. Data represent the mean ± SEM of three separate determinations. The affinity constants of the IGF-I and IGF-II for the type-I and type-II receptors were taken from ref. 34 and 35, respectively, whereas the affinity constants of the IGFBP ligand inhibitor for the IGF receptors were taken from ref. 33.