Human insulin: assembling the mature hormone.

Pro-insulin folding with its C peptide vs Eli Lilly's route: A and B chains made separately in E. coli and joined by disulphide bonds.

Assemble mature human insulin by the Eli Lilly route: both chains present, all three disulphide bridges correct, no C peptide anywhere.

Writing that Eli Lilly's E. coli made pro-insulin with the C peptide.

• Recombinant DNA technology allows mass production of safe and more effective therapeutic drugs. Recombinant therapeutics do not provoke the unwanted immune responses common with similar products taken from non-human sources.
• Worldwide, about 30 recombinant therapeutics have approval for use in humans; 12 of these are currently sold in India.
• Adult-onset diabetes can be managed by taking insulin at regular intervals.
• Insulin was earlier extracted from the pancreas of slaughtered cattle and pigs. Being a foreign protein, animal insulin caused allergy or other reactions in some patients.
• Insulin is made of two short polypeptide chains, A and B, linked by disulphide bridges.
• In mammals, humans included, insulin is made as a pro-hormone that must be processed before it works. The pro-hormone carries an extra stretch, the C peptide, which is removed during maturation and is absent from mature insulin.
• The main difficulty in making insulin by rDNA techniques was getting it assembled into the mature form.
• In 1983 the American company Eli Lilly made two DNA sequences, one for the A chain and one for the B chain of human insulin, and placed them in E. coli plasmids.
• The A and B chains were produced separately, extracted, and joined by creating disulphide bonds, giving human insulin.

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