The insulin receptor is an integral part of plasma membrane of most cells. It consists of 2 alpha and two beta subunits. The alpha subunit is the hormone binding component, while beta subunits are a tyrosine specific protein kinase which itself can be autophosphorylated. Receptor tyrosine kinase activation upon insulin binding catalyses the phosphorylation of exogenous substrates and endogenous cellular proteins. It is reasonable to think that the insulin induced autophosphorylation, activation of its receptor kinase and changes in intracellular substrates represent important events in the action of insulin on cell metabolism and growth.