25/-/GF-/. 125I-IGF-I was bound mainly to three bands of microvillous membrane protein (Fig. 5). The labeled ligand that bound to a slow-moving molecule of molecular mass higher than 250 kDa (B) was displaced by unlabeled IGFI. The main labeled band migrated in the 135-kDa (E) region and was displaced by 200 |xg IGF-I (it became only faintly labeled). The third (130 kDa) band (F) was less intense than the 135-kDa one, but unlabeled competitors affected it in the same way as they did the 135-kDa band.
FIG. 5. Affinity cross-linking of ,25I-IGF-I to binding sites on placental microvillous membranes and basal plasma membranes.
125I-IGF-I bound to four bands of basal plasma membrane protein (B,D,E,F) (Fig. 6). The labeled ligand that bound to a large, slowly migrating molecule (B) was displaced by 200 |xg (0.1 |лМ) unlabeled IGF-I but not to any great extent by IGF-II or insulin. 125I-IGF-I was also bound to a second molecule in the 220-kDa (D) region (Fig. 6) and was displaced by 200 |xg (0.1 |xM) IGF-I but not by IGF-II or insulin. The 125I-IGF-I that bound to a 135-kDa band (E) was displaced by IGF-I but not to any great extent by IGF-II or insulin. 125I-IGF-I bound to a 130-kDa molecular mass band (F) was displaced by IGF-I but by neither IGF-II nor insulin. buy levaquin online
FIG. 6. Affinity cross-linking of l25l-IGF-ll, 125I-IGF-I, and 125l-insulin to binding sites on basal plasma membranes. The labeled ligand at 1.33 nM (250 000 cpm) was incubated with membranes (120-150 jxg protein) either alone or with unlabeled competitors (200 ng of IGF-I or IGF-II, or 10 ixg of insulin). Autoradiography was longer (28 days) than for the Figure 2, 4, and 5 experiments (21 days). Molecular masses above 250 kDa were calculated.