A comparative study on the basic pancreatic trypsin inhibitor and insulin by the hydrogen-exchange method.

Abstract

The 1H–2H exchange in 2H2O solutions, at 25 °C, of the basic pancreatic trypsin inhibitor and of insulin has been studied by infrared and proton magnetic resonance spectroscopy. Under identical conditions of pH the exchange in the peptide groups of the inhibitor is considerably slower than the exchange in the peptide groups of insulin, indicating that the interior regions of the inhibitor molecules are less accessible to the solvent than those of the insulin molecules. The experimental results are expressed in terms of the probabilities of local conformational changes of the proteins, by which the peptide groups are exposed to the solvent, and in terms of the corresponding changes in standard free energy. The data is taken as an illustration of the range of distributions of values of these parameters, typical of globular proteins.