Elongation of the interchain disulfide bridges of insulin.  A synthetic analog.
The sythesis and isolation in purified form of an analog of insulin with the interchain disulfide bridges elongated by a methylene group is described.  This analog differs from the parent molecule in that the cystein residues occupying positions A-7 and A-20 and involved in the formation of the two interchain disulfide bridges of insulin have been replaced by homocysteine residues.  For the synthesis of this compound the Hcy-7, 20-A chain of sheep insulin was chemically synthesized and isolated in the S-sulfonated form.  Conversion of the latter product to the sulfhydryl derivative and combination with the S-sulfonated form of the B chain of sheep insulin yielded the [Hcy-7, 20-A] insulin.  Isolation of the analog from the combination mixture was effected by chromatography on a carboxymethylcellulose column with acetate buffer (pH 3.3) and an exponential sodium chloride gradient.  This analog, by the mouse convulsion assay methods and in doses at least 40-fold higher than those normally used for insulin assay, was inactive.  By the radioimmunoassay method this synthetic analog was found to possess a potency of 2 i.u./mg.  It is concluded that the biological activity of insulin depends critically on a particular geometry conferred on the molecule by the proper placement of the A and B chains.
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001681:Biological Assay; D002417:Cattle; D002850:Chromatography, Gel; D004220:Disulfides; D004586:Electrophoresis; D007328:Insulin / Q000031:analogs & derivatives* / Q000138:chemical synthesis; D051379:Mice; D011863:Radioimmunoassay; D012640:Seizures; D012756:Sheep
D000596:Amino Acids; D004220:Disulfides; D007328:Insulin