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Recombinant Insulin - Successful Application of Genetic Engineering
Insulin is a protein hormone secreted from the specialized cells of the islet of Langerhans in pancreas. Only 2% of the pancreas has endocrine function secreting various types of hormones regulating the metabolism of glucose. Of them, the β cells constitute about 65-80% and they are responsible for the secretion of insulin. It is polypeptide in nature and affects almost all the cells and organs within the body. It affects the metabolism of carbohydrates, fats and proteins and is responsible for various anabolic reactions, which help in lowering the blood sugar level in the blood. Diabetes mellitus has become a very common disease in the present times after cancer and cardiovascular diseases. Hence, the role of insulin and its various aspects have become a topic for serious study and research.

Insulin is a simple polypeptide hormone consisting of 51 amino acids. It is made of two polypeptide chains A and B. A chain consists of 30 amino acids while the B chain consists of 21 amino acids and the two chains are linked by a disulfide bond. The insulin structure and composition varies in different species as the sequence of the amino acids in human insulin is highly conserved. Diabetes mellitus if of two types: Type I, which is an autoimmune disorder characterized by lower insulin levels in the body and Type II in which insulin levels are normal but the body develops peripheral resistance to it resulting in high blood sugar levels. Type I form is a very common disease; hence, different types of treatment to maintain insulin level in the body are being developed. It was seen that the administration of purified animal insulin could not be done as it resulted in immune response. Hence, two forms of treatment was followed, which are: artificial synthesis of insulin using amino acids, which is an expensive and long drawn process and the replacement of amino acids in the purified animal insulin to represent human insulin, known as semi-synthetic insulin. The synthesis of semi-synthetic insulin also faced problems in the form of limited availability of porcine insulin, which was most suitable for the purpose. In this situation, the research on the synthesis of recombinant insulin was carried out to meet the increasing demands for insulin.

Recombinant insulin is the first commercial biotech product. The advances in RDT (Recombinant DNA Technology) with the discovery of various restriction enzymes, cloning strategies, etc has helped in the successful formation of recombinant insulin. The use of recombinant insulin offers two main advantages: unlimited availability of insulin to meet increasing demands of diabetic patients and the identical similarity of human and recombinant insulin. The RDT has used both bacteria and yeast for the recombinant insulin production. The production uses two types of strategies:

i) The synthesis of the two chains of insulin and joining them with disulfide linkage using ideal conditions, and
ii) The synthesis of proinsulin, which then forms mature Insulin after the cleavage of C-peptide and formation of disulfide bond between the two chains.

In the first method, two DNA fragments based on the sequence of the amino acids in the A and B chains were synthesised. These fragments were inserted into plasmids, which were transformed into the bacteria. The two chains were then isolated and mixed under ideal conditions for the formation of disulfide links between them, producing functional Insulin. The other method involved the formation of proinsulin in bacteria, which then formed mature Insulin by a single enzymatic reaction. This was found to be a better procedure due to the lesser number of steps involved in the production and purification of mature insulin. After the formation of recombinant insulin from bacteria, purification is a very essential step as contamination with the C-peptide, proinsulin, etc may cause ineffective result in the use of recombinant insulin. In order to minimise the purification procedure, which may result in the loss of recombinant insulin, the latest technology involves the use of yeast for the production of proinsulin. The enzymes required for the formation of mature insulin like the ones present within the human body are present within the yeast yielding a better formation and isolation of the formed mature insulin from the media, where recombinant yeast is cultured.

Insulin is the first genetically engineered hormone opening the field of research for the generation of other important hormones and proteins for the treatment of different fatal diseases. The advance in genetic engineering technology is becoming the main gateway for the progress of medical science and discovery of helpful drugs for the welfare of living beings.
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