Structural studies on des-pentapeptide (B26-30)-insulin. V. High resolution NMR studies

Preliminary studies have been made of the 250 MHz nuclear magnetic resonance spectra of both insulin and DPI. Differences have been found between DPI and insulin spectra, which indicate that the splitting off of the B-chain C-terminal pentapeptide from insulin has brought about local changes in the conformation of the protein molecule in solution. It seems that these conformational changes have little effect on the biological activity of the hormone. Many studies have revealed that for insulin molecules in solution, an equilibrium exists between aggregation and dissociation, their state of aggregation bearing a close relationship to the concentration as well as pH of the insulin solution. Changes in the concentration and pH value of DPI solutions do not significantly affect the NMR spectra. But as the concentration and pH of the solution are increased, the methyl regions for valine, leucine, and isoleucine and aromatic regions of the insulin spectra are broadened. All these show that zinc-free DPI molecules probably exist as monomers in solution.