Antibodies to Purified Insulin Receptor Have Insulin-Like Activity

Antibodies to insulin receptors purified from rat liver membranes do not complete with 125 Iinsulin for binding to the insulin receptor but do precipitate solubilized receptors labeled with 125 Iinsulin. These antibodies have the insulin-like activities of enhancing glucose oxidation and inhibiting epinephrine-induced lipolysis in rat adipocytes. Thus, antibody binds to the receptor at a different site from that to which insulin binds, yet the interaction can initiate an effective biological response. These results indicate that the previously studied insulin-binding sites are the physiological macromolecular receptors for insulin.