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The cascade that leads to the insertion of GLUT4 glucose transporters into the cell membranes of muscle and fat cells, and to the synthesis of glycogen in liver and muscle tissue, as well as the conversion of glucose into triglycerides in liver, adipose, and lactating mammary gland tissue, operates via the activation, by IRS-1, of phosphoinositol 3 kinase ([[phosphoinositide 3-kinase|PI3K]]). This enzyme converts a [[phospholipid]] in the cell membrane by the name of [[phosphatidylinositol 4,5-bisphosphate]] (PIP2), into [[Phosphatidylinositol (3,4,5)-trisphosphate|phosphatidylinositol 3,4,5-triphosphate]] (PIP3), which, in turn, activates [[AKT|protein kinase B]] (PKB). Activated PKB facilitates the fusion of GLUT4 containing [[endosome]]s with the cell membrane, resulting in an increase in GLUT4 transporters in the plasma membrane. PKB also phosphorylates [[GSK-3|glycogen synthase kinase]] (GSK), thereby inactivating this enzyme. This means that its substrate, [[glycogen synthase]] (GS), cannot be phosphorylated, and remains dephosphorylated, and therefore active. The active enzyme, glycogen synthase (GS), catalyzes the rate limiting step in the synthesis of glycogen from glucose. Similar dephosphorylations affect the enzymes controlling the rate of [[glycolysis]] leading to the synthesis of fats via [[malonyl-CoA]] in the tissues that can generate [[triglycerides]], and also the enzymes that control the rate of [[gluconeogenesis]] in the liver. The overall effect of these final enzyme dephosphorylations is that, in the tissues that can carry out these reactions, glycogen and fat synthesis from glucose are stimulated, and glucose production by the liver through [[glycogenolysis]] and [[gluconeogenesis]] are inhibited. The breakdown of triglycerides by adipose tissue into [[free fatty acids]] and [[glycerol]] is also inhibited.

Translations:Insulin/41/en - Revision history

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