What is Insulin
Insulin is a hormone of protein nature, produced by groups of pancreatic cells, called "β cells of the islets of Langerhans". It was discovered in 1921 by the Englishman John James Macleod and by the Canadian Frederick Grant Bating, Nobel Prize for medicine in 1923.
Functions
Insulin is the anabolic hormone par excellence, in fact through its action:
- facilitates the passage of glucose from the blood to the cells and therefore has hypoglycemic action (lowers blood sugar). Promotes the accumulation of glucose in the form of glycogen (glycogenosynthesis) in the liver and inhibits the degradation of glycogen to glucose (glycogenolysis).
- It facilitates the passage of amino acids from the blood to the cells, it has an anabolic function because it stimulates protein synthesis and inhibits neoglucogenesis (formation of glucose starting from some amino acids).
- It facilitates the passage of fatty acids from the blood to the cells, stimulates the synthesis of fatty acids starting from glucose and excess amino acids and inhibits lipolysis (utilization of fatty acids for energy purposes).
- Facilitates the passage of potassium into the cells.
- Stimulates cell proliferation.
- It stimulates the use of glucose for energy production.
- It stimulates the endogenous production of cholesterol.
The greatest stimulus for insulin action is given by a meal rich in simple carbohydrates and low in fiber, fat and protein. Also some drugs (sulfonylureas) are able to increase their secretion.
Insights
Insulin and sportInsulin and dopingGlycaemia and slimmingDiabetesInsuline resistance hyperinsulinemia Rapid insulin and slow insulin Insulin-based drugsSynthesis
Proinsulin is the biosynthetic precursor of insulin. There is also a pre-pro-insulin that compared to proinsulin has a sequence of amino acids that acts as a signal for its transport, first in the reticuloendoplasmic and then in the Golgi, where it reaches the correct conformation.
Insulin is released as a globular polypeptide chain protein unique to polyribosomes; subsequently the hormone is deposited in the form of granules reaching a crystalline form visible under the electron microscope. As the concentration increases, the insulin is aggregated into dimers (a pair of monomers held together by weak bonds) and dimers or hexamers trimers (held together by 2 central Zaco ions exacoordinated with the 3 tyrosines of the dimers and the three molecules of H2O ).
Once the insulin has been discharged into the circulatory stream, by dilution it passes to the dimeric and monomeric form, the latter being recognized by the insulin receptor.
Some researchers noted that in human insulin there are variable regions, in particular the amino acid sequence n ° 28 and 29 (Pro-Lys) of the β chain; subsequently it was discovered that reversing these AA insulin passed directly to the monometric state, skipping the dimeric one. Thus was born the "Lys Pro" or "rapid insulin", a drug particularly useful if injected near a large meal.
Action mechanism
The insulin receptor is a transmembrane glycoprotein consisting of 4 chains (2α external to the cell and 2β internal to the cell), joined together by sulphide bridges. The molecule has a rather short half-life and is therefore subject to a rapid turnover. It too is synthesized as a precursor by the rough endoplasmic reticulum and is then processed in the Golgi. The 2 α chains are rich in cysteines while the β are rich in hydrophobic AA, which anchor them to the cell membrane, and thyroxine, facing the inner part of the cytosol.
Insulin receptor binding stimulates tyrosine kinase activity and leads to the expenditure of 1 ATP for phosphorylated tyrosine. This causes a series of chain events (activation of the G phospholipase C proteins) that lead to the formation of two products: the DAG that remains anchored to the membrane and that intervenes in the phosphorylation of proteins, and the IP3 that acts at the cytosolic level allowing Ca ++ ion release.
When blood sugar levels rise it increases the amount of insulin secreted by pancreatic cells. In insulin-dependent cells the insulin receptor bond acts on an intracellular pool of vesicles, freeing the glucose transporter which is transferred to the membrane by fusion. Carrying glucose into the cell, causing a decrease in blood sugar which in turn stimulates the dissociation between insulin and its receptor. This dissociation triggers a process of similar endocytosis with which the carrier is brought back into the vesicles.
Diabetes and Insulin
The term diabetes comes from the Greek diabetes and means to pass through . One of the characteristic clinical signs of this pathology is the presence of sugar in the urine, which reaches you through the kidney when its concentration in the blood exceeds a certain value. This term has been associated with the adjective mellitus because the urine, due to the presence of sugar, is sweet and, anciently, tasting was the only way to diagnose the disease
Diabetes mellitus is a chronic disease, characterized by hyperglycemia, that is by an increase in the sugars (glucose) present in the blood. It is caused by reduced secretion of INSULIN or by the combination of reduced secretion and peripheral resistance to the action of this hormone.
Under normal conditions, insulin released by the pancreas enters the bloodstream where it functions as a "key" needed to get glucose into the cells, which, depending on the metabolic demands, will use it or deposit it as a reserve. This explains why a deficiency or an altered insulin action is accompanied by an increase in circulating sugars, a characteristic that is typical of diabetes.
