A preferential binding site for insulin-like growth factor II in human and rat placental membranes.

Abstract

We have compared the binding of insulin-like growth factors I and II (IGF-I and IGF-II) by partially purified human and rat placental membranes. When [125I]IGF-I wasbound by human placental membranes, IGF-I was more effective than IGF-II in displacing the tracer. Scatchard analysis of the binding of IGF-I provided evidence of a high affinity, low capacity binding system and a second lower affinity binding system. When [125I]IGF-II was bound by human placental membranes, it was displaced much more readily by IGF-II than by IGF-I. Scatchard analysis of the binding of IGF-II indicated that the high affinity component of binding was reduced, and most of the binding of IGF-II was due to the lower affinity and higher capacity system. In comparison to human placenta, rat placental membranes bound [125I]IGF-I relatively weakly, the IGF-II was more effective than IGF-I and rat somatomedin in displacing this label. In contrast, the binding of [125I]IGF-II by rat placental membranes was greater than that of [125I]IG...