Human insulin is synthesised as a pro-hormone. The pro-hormone contains an extra C-peptide. The C-peptide is not present in mature insulin, and is removed during maturation, Eli-Lily-an American company prepared two DNA sequences, corresponding to A and B chains of human insulin, and introduced them in plasmids of E. coli to produce insulin chains, Chain A and B were produced separately, extracted and combined, by creating disulphide bonds.
