insulin, hormone hormone, secretory substance carried from one gland or organ of the body via the bloodstream to more or less specific tissues, where it exerts some influence upon the metabolism of the target tissue.
..... Click the link for more information. secreted by the β cells of the islets of Langerhans, specific groups of cells in the pancreas pancreas (păn`krēəs), glandular organ that secretes digestive enzymes and hormones.
..... Click the link for more information. . Insufficiency of insulin in the body results in diabetes diabetes or diabetes mellitus (məlī`təs)
..... Click the link for more information. . Insulin was one of the first products to be manufactured using genetic engineering genetic engineering, the use of various methods to manipulate the DNA (genetic material) of cells to change hereditary traits or produce biological products.
..... Click the link for more information. .

Action

In general, insulin acts to reduce extracellular (including blood plasma) levels of glucose glucose, dextrose, or grape sugar, monosaccharide sugar with the empirical formula C₆H₁₂O₆ .
..... Click the link for more information. by interacting in some way yet unknown with various cell membranes. In adipose (fatty) tissue it facilitates the cellular uptake of glucose and its subsequent conversion to fatty acids fatty acid, any of the organic carboxylic acids present in fats and oils as esters of glycerol . Molecular weights of fatty acids vary over a wide range. The carbon skeleton of any fatty acid is unbranched. Some fatty acids are saturated, i.e.
..... Click the link for more information. , and it inhibits the breakdown of fatty acids to simpler compounds. In muscle it again facilitates the transport of glucose into cells and in addition stimulates its conversion to glycogen glycogen (glī`kəjən)
..... Click the link for more information. . It also increases protein synthesis in muscle. In the liver, insulin facilitates glucose catabolism catabolism (kətăb`əlĭz'əm), subdivision of metabolism involving all degradative chemical reactions in the living cell.
..... Click the link for more information. and its conversion to glycogen and inhibits its synthesis from simpler compounds.

Isolation and Structure

Canadians Frederick G. Banting Banting, Sir Frederick Grant, 1891–1941, Canadian physician, M.D. Univ. of Toronto, 1922. From 1923 he was professor of medical research at Toronto. Working with C. H. Best under the direction of J. J. R.
..... Click the link for more information. and Charles H. Best Best, Charles Herbert, 1899–1978, Canadian physiologist, b. West Pembroke, Maine. With F. G. Banting he discovered (1921) the use of insulin in the treatment of diabetes. He was appointed professor of physiology at the Univ.
..... Click the link for more information. were the first to obtain, from extracts of pancreas (1921–22), a preparation of insulin that could serve to replace a deficiency of the hormone in the human body. The complete amino acid sequence of the insulin molecule was described in the early 1950s; insulin was the first protein to be sequenced entirely. This pioneering work was confirmed from 1963 to 1966, when several groups reported laboratory synthesis of biologically active insulin. The three-dimensional structure of the crystalline hormone was published in 1969.

Insulin has been shown to be a protein consisting of two polypeptide chains (see peptide peptide, organic compound composed of amino acids linked together chemically by peptide bonds. The peptide bond always involves a single covalent link between the α-carboxyl (oxygen-bearing carbon) of one amino acid and the amino nitrogen of a second amino acid.
..... Click the link for more information. ), one of 21 amino acid residues and the other of 30, joined by two disulfide bridges (see cysteine cysteine (sĭs`tēn), organic compound, one of the 20 amino acids commonly found in animal proteins .
..... Click the link for more information. ). The two chains are synthesized in the β cells as part of one continuous polypeptide chain called proinsulin; a 32-amino acid sequence (the connecting peptide) is subsequently split out of the proinsulin molecule by an enzyme resembling trypsin trypsin, enzyme that acts to degrade protein ; it is often referred to as a proteolytic enzyme, or proteinase. Trypsin is one of the three principal digestive proteinases, the other two being pepsin and chymotrypsin .
..... Click the link for more information. to yield active insulin.

Insulin in Diabetes Treatment

Many, but not all, of the symptoms of diabetes can be controlled by the administration of insulin. The forms of insulin available early in the 20th cent. had to be injected frequently because they were quick-acting. Later modifications gave the insulin solution a more prolonged action so that hypodermic injections could be made less frequently. Some now control their insulin levels via a small, portable insulin pump. In certain cases of mild diabetes, oral medications that stimulate production of insulin can be taken in lieu of insulin. See glucagon glucagon (gl
..... Click the link for more information. .

insulin

Polypeptide hormone (see peptide) that regulates blood glucose levels. Secreted by the islets of Langerhans (see Langerhans, islets of) in the pancreas when blood glucose rises, as after a meal, it helps transfer the glucose into the body's cells to be oxidized (see oxidation-reduction) for energy or converted and stored as fatty acids or glycogen. When blood glucose falls, insulin secretion stops and the liver releases more glucose into the blood. Insulin has various related functions in the liver, muscles, and other tissues, controlling the balance of glucose with related compounds. Insulin-related disorders include diabetes mellitus and hypoglycemia. Frederick Banting and J.J.R. Macleod won a Nobel Prize in 1923 for discovering insulin, and Frederick Sanger won one in 1958 for determining its amino acid sequence.