Binding of insulin dimers to receptors

A synthesis of current views of the nature of the self-association of insulin in solution, of the identity of the amino acid residues in the insulin molecule constituting the receptor binding site, and of characteristics of the apparent 'negative cooperativity' of the binding leads to the seemingly contradictory conclusions that only the monomeric form of the protein is available and capable of binding, yet that other species must bind as well. A solution that has been proposed is that an alternative binding site exists, one which is not involved in insulin dimerization. Here, these conclusions are re-examined in the light of the characteristics of a new model for the polymerization of insulin. Firstly, it is found that the idea that dimers and higher polymers of insulin can bind to receptors is plausible, even necessary, secondly, that the postulate of an alternative binding site on insulin molecules is not required, and finally, that the characteristics of the insulin-receptor interaction warrant further investigation specifically in terms of the ability of some insulins to polymerize in solution and their potential to cross-link receptors.