The Role of Protein Phosphorylation in Insulin Action
It has been well established that insulin exerts numerous effects on the metabolism of carbohydrates, lipids and amino acids as well as on membrane transport processes and protein synthesis. However, in spite of extensive studies the mechanism of insulin action at the molecular level is an unsolved problem (Walaas and Horn, 1981). At the present time there is general agreement that the initial event in insulin action involves interaction of the hormone with specific receptors in the plasma membrane of target cells. The receptor has now been purified and has a molecular weight of 350,000. The protein consists of two α-subunits (Mr 135,000) and two β-subunits (Mr 95,000) associated by disulfide bridges (Czech et al., l981). The coupling system between the insulinreceptor complex and intracellular effector systems has yet to be elucidated. For many years research in this field has been concerned with identification of a “second messenger” of insulin action. A series of small molecules including cyclic AMP, cyclic GMP, unknown nucleotides, Ca2+ , H2O2, etc. have been proposed as mediators of insulin action. Until now these investigations have failed to identify a specific insulin dependent coupling system.
KeywordsInsulin Action Protein Phosphorylation Pyruvate Dehydrogenase Rabbit Skeletal Muscle Phosphoprotein Phosphatase
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