Structural studies on des-pentapeptide (B26-30)-insulin. IV. A preliminary investigation on the hydrophobic region by employing a fluorescence probe, 1-p-toluidinylnaphthalene-8-sulphonate.

The fluorescnece porperties of 1,8-TNS in relation to the polarity and viscosity of the solvents have been studied and found to be just as useful as those of its positional isomer 2,6-TNS in the capacity of being a fluorescent probe. The properties of the hydrophobic region of insulin, des-pentapeptide (B26-30)- insulin (DPI), bovine plasma albumin, lysozyme, and ovalbumin have been investigated by employing this fluorescent probe. It has been shown that there is a small but definite hydrophobic region in DPI just as in insulin. This suggests that removal of the C-terminal pentapeptide does not impair seriously the hydrophobic structure related to the binding with insulin receptor. However, at physiologic pH, the hydrophobic region of DPI becomes more exposed than that of insulin and its conformation is less stable. As the pH is increased, the local conformation of the DPI molecule probably suffers some distortion, which damages the conformation of the hydrophobic region to a certain extent. In comparison with insulin, the DPI molecule is relatively loose and unstable.