Measurement and Computation of the Dipole Moment of Globular Proteins. 4. α- and γ-Chymotrypsins

Abstract

The dipole moments of α- and γ-chymotrypsins are determined using the dielectric constant measurement. The results are roughly comparable to those of electric dichroism measurements despite the principle and methodology of these two techniques are entirely different. Nevertheless, the differences which exist between them seem to be beyond the experimental error. The cause of disagreement appears to be, at least partially, due to the difficulty of finding the correct internal field. A new theory which is based on an ellipsoidal particle surrounded by a hydration shell is discussed. The model was found to improve the agreement markedly. Additionally, in order to corroborate the observed dipole moments with numerical computations, the dipole moments of α- and γ-chymotrypsins were calculated using protein data bases. The dipole moment of small proteins consists of two major components, the moment due to fixed surface charges and the core moment due to polar chemical bonds. The calculation of the surface charg...