Assembly of insulin/insulin-like growth factor-1 hybrid receptors in vitro*

Insulin and Mn/MgATP treatment of immunoaffinity-purified αβ heterodimeric insulin receptors induced the formation of an α2β2heterotetrameric insulin receptor complex. In contrast, insulin-like growth factor-1 (IGF-1) treatment was completely ineffective in inducing the association of αβ heterodimeric insulin receptors. Similarly, IGF-1 or Mn/MgATP, but not insulin, treatment of immunoaffinity-purified αβ heterodimeric IGF-1 receptors induced the formation of an α2β2heterotetrameric IGF-1 receptor complex. A monoclonal antibody specific for the insulin receptor (MA5) completely immunoprecipitated all the insulin binding activity from both the α2β2heterotetrameric and αβ heterodimeric insulin receptor complexes but did not immunoprecipitate IGF-1 receptors. Conversely, the IGF-1 receptor-specific monoclonal antibody (αIR-3) immunoprecipitated all the IGF-1 binding activity, but not insulin receptors.