Characterization of affinity-purified type I insulin-like growth factor receptor from human placenta

The binding affinities of type I IGF receptor, purified to near homogeneity from human placental membranes, were characterized. For this receptor preparation, free of type II IGF receptor and essentially free of insulin receptor, dissociation constants of Kd = 0.05 nM for IGF I and of Kd = 0.2 nM for IGF II (linear Scatchard plots) were determined. Competitive binding studies indicated a cross-reactivity of approximately 40% for IGF II to the type I IGF receptor.