title: Separation of the two double-chain bovine intermediates of the proinsulin-insulin conversion I. Chemical, immunochemical, circular dichroism, and biological characterization.
abstract: The intermediates of the proinsulin-insulin conversion were separated by cation exchange. The circular dichroism spectra of the intermediates showed less alpha-helix than insulin and proinsulin. It is suggested that the C-peptide interacts with the section of alpha-helix contained between residues 2 and 8 in the A-chain of the insulin moieties and unwinds the alpha-helix. The in vivo activities of the intermediates were found to be in the order of 50% relative to insulin. In the fat cell assay, the A-chain-substituted form is weaker (9%) than the B-chain-substituted form (19%). The C-peptide segments of the two forms reacted with C-peptide-specific antibodies as fully as the free C-peptide, on a molar basis. In contrast, the insulin segments were hindered from reacting with insulin-specific antibodies as fully as the insulin.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D000937:Antigen-Antibody Reactions; D001681:Biological Assay; D002417:Cattle; D002942:Circular Dichroism; D003460:Crystallization; D004589:Electrophoresis, Disc; D007328:Insulin / Q000032:analysis* / Q000276:immunology; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D011384:Proinsulin / Q000032:analysis* / Q000276:immunology
chemical_list: D000596:Amino Acids; D007328:Insulin; D011384:Proinsulin