Insulin-induced Dissociation of Its Receptor into Subunits: Possible Molecular Concomitant of Negative Cooperativity

The detergent-solubilized avian insulin receptor retains negative cooperativity and other binding properties of the membrane bound form. On gel filtration the receptor elutes as a single peak with a Stokes radius of 72 A. Preincubation of the receptor with low levels of insulin leads to the formation of a second, smaller form with a Stokes radius of 40 A. The percent of receptor in this second peak is proportional to the insulin concentration and correlates well with the insulin-induced increase in dissociation rate (negative cooperativity). Both the isolated high molecular weight and the isolated low-molecular-weight forms of the receptor re-equilibrate in the presence of insulin and, upon refiltration of either isolated peak, both forms of the receptor are obtained. These results are compatible with a model of the insulin receptor in which a tetrameric form can dissociate to a monomeric form as a concomitant of negative cooperativity.