Calcium-dependence of insulin receptor phosphorylation

Phosphorylation of the insulin receptor of isolated rat adipocytes in response to insulin has been studied. Immunoprecipitation of adipocyte membrane protein demonstrated increased incorporation of 32P after exposure to insulin for 15 min, but this was dependent on the presence of physiological concentrations of Ca2+ and Mg2+. Autoradiography of solubilized immunoprecipitated membrane protein after sodium dodecyl sulphate/polyacrylamide-gel electrophoresis revealed that most of the 32P incorporation occurred in a band corresponding to Mr 95 000, which has been identified previously as the beta-subunit of the insulin receptor. 32P incorporation was inhibited by 2,4-dinitrophenol and trifluoperazine. It is suggested that insulin-receptor phosphorylation is an energy-requiring process that is Ca2+-dependent and may be modulated by calmodulin. Phosphorylation may proceed independently of glucose transport.