Characterization of two insulin-binding components of rat-liver plasma membranes

We have identified and isolated two forms of insulin receptor from rat-liver plasma membranes. The smaller (Mr = 90k) is a single polypeptide. The same polypeptide appears to be the insulin-binding site of the larger Mr = 280k). Only the larger, multisubunit, receptor shows high-affinity binding of insulin and negative cooperativity in its dissociation kinetics.