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

Insulin in the presence of Mn2+ and [gamma 32P]ATP promoted the phosphorylation of two proteins of Mr 95 000 and Mr 210 000 in detergent extracts of rat liver microsomes. The Mr 210 000 protein was identified as a component od 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 Mr 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.