Insulin Production

Human insulin production by genetic engineering Insulin hormone is produced by beta cells of islets of langerhans of pancreas which catabolise glucose in blood. It consists of 2 polypeptide chains which are 21 aminioacids long and 30 aminoacids long. Proinsulin is a precursor of 109 amino acids that contains 2 polypeptide chains A and B connected with a third polypeptide chain. The peptide hormone genes of the specialized cells encode for a 35 aminoacid long chain. Pre proinsulin can be used for regulation of glucose in diabetic patients. Experiments were conducted on rats to synthesize the cDNA of the proinsulin by isolating mRNA and inserting it into the plasmid vector. Itakura et. al in 1977 synthesized A and B chains of insulin by using pBR322 plasmid containing beta-galactosidase beside it. The recombinant plasmids could separately produce the fused beta-galactosidase A and B chains in the E. coli cells with plasmid vectors. Both the chains that were produced in different cells were made free of the beta-galactosidase enzyme and pure form in an amount of 10mg/ 24mg of healthy and transformed cells was obtained. The addition of an extra methionine codon at the N- terminus of A and B chain genes was performed for detaching the A and B chains respectively. After detachment of beta-galactosidase linked A and B chain in the cells, the two chains were joined invitro to reconstitute the native form of insulin. This was brought about by the process of sulphonation using sodium disulphonate and sodium sulfite.

Hybrid forms of insulin protein were developed in due course such as penicillinase and proinsulin fused forms. By inserting the proinsulin gene in the middle of the pencillinase gene coding site present in the pBR322 plasmid. The fused form of proinsulin was separated by using trypsin. The first therapeutic product of human insulin was produced by Eli Lily’s and coworkers in 1980. Each bacterial cell of E.coli is capable of producing nearly 1 million molecules of insulin. A genetically engineered form of insulin is quite effective and has no side effects. It is available commercially since 1982 for the benefit of mankind