Insulin binds to and promotes the phosphorylation of a M r 210 000 component of its receptor in detergent extracts of rat liver microsomes

Abstract
Insulin in the presence of Mn2+ and [γ32P]ATP promoted the phosphorylation of two proteins of M r 95 000 and M r 210 000 in detergent extracts of rat liver microsomes. The M r 210 000 protein was identified as a component of the insulin receptor by immunoprecipitation. It also bound [125I]insulin specifically, was phosphorylated largely on a tyrosine residue and could not be cleaved to smaller subunits under extreme reducing conditions. The M r 210 000 protein appears to be a component of a sub-population of liver membrane insulin receptors in which insulin-binding and insulin-stimulated tyrosine kinase phosphorylation site(s) reside in a single polypeptide chain.