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i.Insulin: is used for the treatment of diabetes and was earlier extracted from pigs and cattle which had some side effects due to additional contaminating compounds, whereas, the recombinant insulin, introduced into the market in 1982, produced by recombinant E. coli has no such problems. Banting and Best discovered and isolated insulin from the dog’s pancreas. F. Sanger (1955) (fourth person in the world who was awarded Nobel Prize two times; the first one in chemistry, for giving the structure of insulin in 1958 and the second for ‘di-deoxy chain termination method of DNA sequencing’ in 1980) gave the amino acid sequence of insulin and was awarded Noble Prize (Fig. 20.1). It is made up of 2 polypeptides – one is 21 amino acids long and the other is 30 amino acids long (total 51 amino acids).

Fig, 20.1 Frederick Sanger

ii.  Somatostatin: is a growth hormone and is a protein which was introduced into the market in 1985. It is extremely difficult to isolate from the animals (about 0.005 g hormone is isolated from 0.5 million sheep brains). After cloning of the human growth hormone gene in E. coli, the yield has been increased many times (0.005 g/L bacterial fermentation medium). It is used for the treatment of hypopituitary dwarfism which is caused due to growth hormone deficiency (about 1 child in 5000). The hormone improves the muscle growth and is exploited by some athletes.

iii. Interferons: They were discovered by two British researchers, Issacs and Lindenrnann in 1957. They have been named interferons as they interfere with the virus infection by inducing the degradation of viral mRNA in infected cells by the enzyme ribonuclease. Human interferons are glycoproteins (protein-sugar) and are produced by virus infected cells in order to protect healthy cells. They control a large number of viral diseases, e.g., common cold, cancer, etc. They have potential application in cancer therapy as they attack cancer cells by inhibiting their growth (division). They also check the growth of cancer virus, AIDS virus, hepatitis-B virus, etc. The protection conferred by them is non- specific (interferons induced by one virus can provide protection against other viruses also). They have not become the antibiotics of the viral infections because minute amounts of interferons are produced in the cells and, moreover, their isolation extraction) from other cellular proteins is complicated. Conventionally, they were obtained from human blood. Currently they are produced from cultured mouse fibroblasts or human leucocytes infected with Sendai virus and genetically engineered bacteria (E. coli) or yeast with inserted gene for human fibroblast interferon, which are more pure and much cheaper (about 11150 cost of the conventional method).