In 1954, F. Stengler deciphered the primary structure of the insulin molecule, which was the first protein of known amino acid sequence. As it turned out, insulin consists of two polypeptide chains, differing in the number of amino acid residues, and connected by a pair of disulfide bonds. Insulin is a low molecular weight polypeptides, its structure determines the correct receptor interaction and display of biological action.
The synthesis of insulin by the pancreas
The B-cells of the islets of Langerhans in their endoplasmic reticulum, preproinsulin is synthesized that contributes to the transformation of stem cells
Stem cells: on the edge of scandal
in B cells. When the signal is split off from the preproinsulin polypeptide, it is converted to proinsulin. This process takes about fifteen minutes. Flakes signal polypeptide regulates B-cell regeneration.
In the Golgi apparatus using proteases for half cleaved from the proinsulin C-peptide, and after three hours a small secretory granules mature active insulin crystals. Two days later insulin matures, they accumulate in the secretory granules are formed. C-peptide is essential to prevent the development of diabetes complications, stabilizing microcirculation.
Ready to insulin is stored in more than ten thousands of secretory granules in the cells of the pancreas. One pellet contains about three hundred thousand molecules of insulin.
The secretion of insulin
Secretory granules containing active insulin migrate to the membrane of B cells are fused with it dissolving in the place of contact than provide exit insulin outwardly. Yield of insulin contribute calcium ions which facilitate exocytosis and affect the function of contractile proteins.
Insulin secretion is also regulated by the nervous system: the sympathetic nervous system inhibits the secretion of insulin and parasympathetic - increases. The release of insulin is at a minimum in all forms of stress
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When demand increases carbohydrates and fats, such as neural and physical stress, as well as during fasting.
Home regulatory role in the secretion of insulin given to food stimuli. Coming from the gastrointestinal tract glucose promotes greater release of insulin have been further activates secretion of other hormones, such as glucagon, secretin, gastrin, and enteroinsulyarnuyu stimulating insulin secretion.
The action of insulin
Insulin exerts its action through the appropriate receptors, the half-life of about ten hours, that is, they are in a constant process of synthesis and degradation. Insulin receptors are found in virtually all cell types, differing in amount, for example, in liver cells of these receptors more than one hundred thousand, and the erythrocytes - only forty.
The main function of insulin - lowering glucose levels
Glucose: The energy source
in the blood by enhancing its absorption by cells of tissues, activation of glycolysis, increased glycogen synthesis and decreased gluconeogenesis. Insulin increases amino acid uptake by cells, enhances transport of ions of potassium, magnesium and phosphorus in the cells, increases protein synthesis and DNA replication, reduces the degradation of proteins and affects lipolysis.
Glucose and insulin transports other substances to the B cells of the pancreas
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Where they are metabolised to form ATP. Insulin itself half of metabolized in the liver, and in sufficient quantity - kidneys.
Not long ago discovered that red blood cells have the ability to bind excess insulin, giving it if necessary into the bloodstream than is stabilized in the body active concentrations of this hormone.
Svetlana Shimkovich
