IlGF_like family, insulin_bombyxin_like subgroup. Members include a number of peptides including insulin, insulin-like growth factors I and II, insect prothoracicotropic hormone (bombyxin), locust insulin-related peptide (LIRP), molluscan insulin-related peptides 1 to 5 (MIP), and C. elegans insulin-like peptides. With the exception of insulin-like growth factors, the active forms of these peptide hormones are composed of two chains (A and B) linked by two disulfide bonds; the arrangement of four cysteines is conserved in the "A" chain: Cys1 is linked by a disulfide bond to Cys3, Cys2 and Cys4 are linked by interchain disulfide bonds to cysteines in the "B" chain. This alignment contains both chains, plus the intervening linker region, arranged as found in the propeptide form. Propeptides are cleaved to yield two separate chains linked covalently by the two disulfide bonds.
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