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From Proteopedia
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Insulin
Introduction
The major function of Insulin is to counter the action of a number of blood sugar generating hormones and to maintain low glucose levels. Because there are numerous high blood sugar hormones, disorders associated with insulin usually lead to severe high blood sugar and other complications. In addition to its role in regulating glucose metabolism, insulin brings about the creating of fat cells, decreases the breakdown of lipids, and increases amino acid transport into cells. Insulin also regulates transcription and stimulates growth, DNA synthesis, and cell replication.
Insulin is synthesized in the β-cells of the islets of Langerhans. Its signal peptide is folded to its basic structure and locked in this conformation by the formation of 2 disulfide bonds. Insulin secretion from β-cells is principally regulated by glucose levels. Increased uptake of glucose by pancreatic β-cells leads to a complementary increase in metabolism. The increase in metabolism leads to the inhibition of an ATP-sensitive potassium channel (KATP channel). The net result is insulin secretion. This role of KATP channels in insulin secretion presents a target for treating high blood sugar due to insulin insufficiency as is typical in type 2 diabetes.
When glucose enters the cells it is used in the respiratory cycle and glycolysis. During this process many high-energy ATP molecules are produced by oxidation, raising the ATP:ADP ratio. This ratio triggers the closing of potassium channels as the cell membrane depolarizes, which then opens calcium channels allowing extracellular calcium to flow into the cell. It is this concentration change that then triggers the release of synthesized insulin. There are many other factors that trigger the release of the insulin hormone from the pancreas, but this is the most common.
Insulin is crucial in maintaining blood glucose levels and the homeostasis of the body that stems from this value. Insulin drives the storage of glucose in the liver and muscle tissue in the form of glycogen, which is also the clinical use of insulin in reducing high blood glucose levels that can branch from diabetes. Insulin also helps to control fatty acid synthesis, proteolysis, gluconeogenesis, esterification, lipolysis, and arterial muscle tone, making it a vital hormone in the overall workings of the body and general health.
PDB Entry
Structure
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