The human placenta contains two distinct binding and immunoreactive species of insulin-like growth factor-I receptors

Abstract

Two species of insulin-like growth factor-I (IGF-I) receptors in human placenta have been delineated on the basis of their immunoreactivity with an autoantiserum (B-2) to the insulin receptor. When all the IGF-I binding sites in solubilized human placenta were assayed by polyethylene glycol precipitation, a curvilinear Scatchard plot was obtained which could be resolved into two single classes of binding sites: one immunoprecipitable by B-2 IgG and the other, nonimmunoprecipitable. The B-2 reactive sites bound IGF-I with lower affinity [K(d) = 7.1 x 10-10 M] than the B-2 nonreactive sites [K(d) = 2.1 x 10-10 M] and cross-reacted more readily with insulin, the IGF-I/insulin-binding potencies ..