Unique spatial compartmentalization of insulin signal transduction. Insulin receptor uses IRS proteins to activate PI3-kinase. Activated insulin receptor binds transiently IRS proteins, which becomes phosphorylated and thereafter bind the regulatory subunits (p85) of PI3-kinase. The IRS-1/PI3-kinase complex translocates to internal membranes, which provide abundant substrates for PI3-kinase and are in close proximity to the GLUT4 vesicle pool, which translocates to the plasma membrane in response to insulin.