Light-scattering Studies of the Interaction between Bovine Serum Albumin and Guanidine Hydrochloride in Aqueous Solutions

The denaturation of bovine serum albumin (BSA) by guanidine hydrochloride (GuHCl) was studied by means of the light-scattering method. The Zimm plots were curved so that apparently imaginary values of the radius of gyration were obtained, but the modified Zimm plots, drawn by applying the correction factor for the optical anisotropy of segments, gave reasonable values of the weight-average molecular weight, the radius of gyration, and the second virial coefficient. The correction factor was calculated by using the experimental values of the scattering ratio at 90° of the scattering angle. The analysis of the intrinsic viscosity showed that the BSA molecules were elongated. According to these results, it has been concluded that the BSA molecules are streched by the denaturation the more as the GuHCl concentration is higher, and that the denatured BSA molecules, at first, form dimers by the side-by-side aggregation of two molecules, but that the intermolecular bindings, too, are broken with the further addition of GuHGl. The length reached at 5m GuHGl was about 1/5 of the fully stretched length. This suggests the possibility that the denatured BSA molecules can keep their local natural conformations.