Introduction of Insulin

Insulin Insulin is a protein hormone. Insulin is secreted by pancreatic islet β cells. In the human body next to the duodenum, there is an elongated organ, called the pancreas. In the pancreas there are many cell groups scattered, called the islets. Pancreas islet in the total number of about 100 to 200 million.

Islet cells according to their function of secreting hormones are divided into the following categories:

1). β cells, accounting for about 60% to 80% of islet cells, insulin secretion, insulin can lower blood sugar.

2). α cells, accounting for about 24% to 40% of pancreatic islet cells, secretion of glucagon, glucagon with the opposite role of insulin, can increase blood sugar.

3). D cells, accounting for about 6% of the total number of islet cells 15%, growth hormone secretion of hormones.

Diabetic patients, due to viral infection, genetic, autoimmune and other pathogenic factors, the pathophysiology of insulin activity is mainly due to relative or absolute deficiency and glucagon activity relative or absolute excess due, that is, B and A cells Bilateral hormone dysfunction caused. Insulin-dependent diabetes mellitus insulin-secreting cells seriously damaged or completely absent, endogenous insulin secretion is very low, need to use exogenous insulin therapy. Non-insulin-dependent diabetes mellitus, insulin secretion disorders lighter, basal insulin concentration normal or increased, and sugar stimulated insulin secretion is generally lower than the corresponding weight, that is, insulin is relatively insufficient.

Discovery process of Insulin

Insulin was first discovered in 1921 by Canadians F.G. Banting and C.H. Best. 1922 for clinical use, so that the past died of diabetes patients to be saved. Institute of Nephrology, Chinese Academy of Sciences attending until the early 80s, almost all of the clinical insulin from pigs, bovine pancreas extracted. Insulin composition of different animals are different, pig and human insulin structure is most similar, only the B-chain carboxyl terminal of a different amino acid. The early 80s have been successful use of genetic engineering technology from microbial mass production of human insulin, and has been used in clinical.

1955 British F. Sanger group determined the entire amino acid sequence of bovine insulin, opened up the human understanding of protein molecular chemical structure of the road. On September 17, 1965, Chinese scientists synthesized synthetic bovine insulin with full biological activity. It was the first protein to be synthesized in the laboratory. Later on, scientists in the United States and the Federal Republic of Germany completed a similar jobs.

In the early 1970s, scientists in the UK and China succeeded in determining the steric structure of porcine insulin by X-ray diffraction. These work laid the foundation for the further study of the relationship between structure and function of insulin molecules. People with chemical synthesis and semi-synthetic analogues prepared to study the impact of its structural changes on biological function; different species of insulin to compare the study; study of abnormal insulin molecule disease, that is due to insulin gene mutation to insulin molecules in individual amino acids Change caused by a molecular disease. These studies also have important practical implications for elucidating the etiology of certain diabetes mellitus.

Insulin secretion process

Insulin Insulin is synthesized in pancreatic islet B cells. Insulin synthesis of the control gene on the 11th chromosome short arm. Genes are normal insulin structure is normal; if the gene mutation is generated by the insulin structure is not normal, for the variation of insulin. In the B cell nucleus, the 11th on the short arm of the genomic DNA on the insulin gene to mRNA transcription, mRNA shift from the nucleus to the cytoplasm of the endoplasmic reticulum, translated into amino acid-linked long peptide - proinsulin, proinsulin The original protein hydrolysis in addition to its propeptide, proinsulin. Proinsulin with the cytoplasm of the micro-bubble into the Golgi body, composed of 86 amino acids long peptide - proinsulin in the Golgi by protease hydrolysis of insulin and C peptide, secreted into the B cells, into the blood circulation. Without protease hydrolysis of proinsulin, a small part of the insulin into the blood circulation, the biological activity of proinsulin and insulin only 5%.

The molecular weight of insulin 5700, composed of two amino acid peptide chain. A chain has 21 amino acids, B chain has 30 amino acids. A-B chain between two disulfide bonds. Islet B cells in insulin reserves of about 200U, daily secretion of about 40U. Fasting, plasma insulin concentration is 5 ~ 15U / mL. Plasma insulin levels after meals can increase 5 to 10 times. The biosynthetic rate of insulin is affected by the plasma glucose concentration. When the blood glucose concentration is increased, the content of proinsulin in B cells increases and the synthesis of insulin is accelerated. In this case, Insulin is secreted into the bloodstream with C-peptide by equivalent molecules. Clinical insulin treatment of patients, the presence of insulin antibodies in serum, radioimmunoassay method to determine serum insulin levels, in this case can be measured by plasma C peptide levels, to understand the status of endogenous insulin secretion.

The main role of Insulin

Insulin main role in the liver, muscle and adipose tissue, control of protein, sugar, fat metabolism and storage of three major nutrients.

(1) the impact of glucose metabolism. Can accelerate the use of glucose and inhibition of glucose production, even if the increase in blood glucose pathways to reduce the source, so blood sugar decreased.

① accelerate the use of glucose. Insulin can improve the permeability of cell membrane to glucose and promote the transport of glucose from the extracellular to the cell. It can also promote the activity of glucokinase (intrahepatic) and hexokinase (extrahepatic), promote the glucose Into glucose phosphate 6, thereby accelerating the glycolysis and oxidation of glucose; and glycogen synthase in the role of glycogen and muscle glycogen to promote the synthesis and storage.

② inhibition of glucose production, can inhibit glycogen breakdown into glucose, and inhibition of glycerol, lactic acid and amino acids into glycogen, reducing gluconeogenesis.

(2) the impact of fat metabolism. Promote the synthesis and storage of fat, inhibit fat decomposition. Diabetes, glucose metabolism disorders, a large number of fat mobilization, resulting in a large number of free fatty acids in the liver oxidation to acetyl coenzyme A, and then into the ketone body, ketone body if there are too many ketoneemia. Insulin can inhibit lipolysis, and promote the use of sugar, thereby inhibiting ketone production, correct ketoneemia.

(3) the impact of protein metabolism. Promote protein synthesis, prevent protein decomposition.

(4) insulin can promote potassium ions and magnesium ions through the cell membrane into the cell; can promote DNA (DNA), ribonucleic acid (RNA) and adenosine triphosphate (ATP) synthesis.

In addition, the glucose in the red blood cells and brain cell membrane out of glucose reabsorption in the renal tubular epithelial cells and small intestinal absorption of glucose, are not affected by insulin. The target cells of insulin action are mainly liver cells, adipose cells, muscle cells, blood cells, lung and kidney cells, testicular cells.