What is Insulin does not facilitate glucose uptake in the following except and explain in detail?
1. Insulin Receptors - Insulin acts by binding to a plasma membrane receptor on the target cells. In obesity, the number of receptors are decreased and target tissue becomes less sensitive to insulin (diabetes mellitus Type 2). Insulin receptor is a glycoprotein with 4 subunits; 2 alpha and 2 beta subunits. The alpha units (135 kD) are located on the extracellular side, to which insulin binds. The beta subunits (95 kD) traverse the membrane and are exposed on the cytoplasmic side. Beta subunit has tyrosine kinase activity. Signal Transduction - Insulin binds to the alpha subunit of the receptor. Oligomerization of alpha units whould trigger the tyrosine kinase activity of the beta subunit. The phosphorylated sites act as docking sites for insulin receptor substrates -IRS1 and IRS2. This recruits GLUT4 to cell surface and stimulate glycogen synthesis. Ref:DM VASUDEVAN TEXTBOOK OF BIOCHEMISTRY, EIGHTH EDITION, PG.NO.,165,166.