Kerr effect study of the aqueous solutions of three globular proteins

A Kerr effect study is reported in which measurements have been made on the magnitudes of both the steady maxima and the decays of the birefringence of solutions of ovalbumin, bovine γ‐globulin, and β‐lactoglobulin. For each protein, results are presented on solutions covering the concentration range of 0.3–1.7 g./100 ml. in order to obtain by extrapolation, values of the specific Kerr constant K sp , and the birefringence relaxation time τ 25, w at zero concentration. The relaxation times thus obtained for ovalbumin (18.3 nsec.) and γ‐globulin (157 nsec.) have been shown to be compatible with molecular models and dimensions presented in the literature. All experiments showed the need for careful extrapolation to zero concentration if reliable parameters are to be obtained: for example a 1% solution of ovalbumin or l.5% solution of γ‐globulin, would give values for τ which are 50% too high when compared with the true value at infinite dilution. The gradual fall in τ for γ‐globulin as the pH was lowered from 6.7 to 3.0 was also studied for three solvents. Fisher's generalized model for the arrangement of the polar residues around the outside of a globular protein has been developed to account for ellipsoidal particles and has been used to demonstrate the suitability and usefulness of this treatment in predicting the conformation and dimensions of these proteins. Rather unusual birefringence traces for β‐lactoglobulin were obtained, which may indicate the dissociation of aggregates, or of the parent molecule into its subunits, under the influence of strong electric fields.