Early steps in insulin action.

The biological effects of insulin are initiated by the binding of insulin to the insulin receptor. Insulin binds to the extracellular domain of the insulin receptor and induces conformational changes in the receptor, leading to autophosphorylation of the receptor on intracellular tyrosine residues. These phosphorylated tyrosine residues act as binding sites for proteins which subsequently may be phosphorylated by the insulin receptor. As a result, yet other proteins can be recruited to form larger complexes and, in the case of enzymes, changes in their activity may take place. By a combination of these processes, the activated insulin receptor initiates cascades of biochemical events which are regulated mainly by specific phosphorylation or dephosphorylation reactions. Intermediates which are involved in the normal insulin signalling pathway are subjects of expanding research.