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 [bovine] insulin and proinsulin. C-peptide probably 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 [in mice] were 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 2 forms reacted with C-peptide-specific antibodies as fully as the free C-peptide, on a molar basis. The insulin segments were hindered from reacting with insulin-specific antibodies as fully as the insulin. [Human albumin, anti porcine insulin, guinea pig serum and anti ox proinsulin guinea pig serum were used].