FOURIER-TRANSFORM INFRARED CONFORMATIONAL STUDY OF BOVINE INSULIN IN SURFACTANT SOLUTIONS

To obtain conformational data on the monomeric form of insulin, which is believed to be the physiologically active form of the hormone, insu lin in sodium dodecyl sulfate solution was studied by Fourier-transfor m infrared (FTIR) spectroscopy and circular dichroism, and results wer e compared with those obtained with des (B23-30) octapeptide insulin ( DOI) and dimeric insulin in buffer. The FTIR amide I band (1600-1700 c m(-1)) was examined, and a quantitative evaluation of the secondary st ructure fractions of the various conformations showed less of a beta-s heet component for both insulin in SDS and DOI in buffer than for insu lin in buffer, corresponding to a lack of monomers binding to form dim ers. At the concentrations used for FTIR (greater than or equal to 2 m g/mL), the CD spectra of insulin in SDS and DOI in buffer were qualita tively identical but different from that of insulin in buffer, which i s associated at these concentrations. The CD spectrum pattern of insul in in very dilute solution (80 nM), where it is prevalently monomeric, is very similar to that of monomeric insulin in SDS, which suggests t hat the conformation of the hormone in the two cases is very similar. (C) Munksgaard 1996