Molecular interactions of bovine serum albumin in electrolyte solutions studied by dynamic light scattering

The concentration dependence of the diffusion coefficient of particles suspended in solution depends primarily on the occupied volume fraction and on repulsive and attractive forces. This dependency is expressed by the interaction parameter. In the present work we have measured the diffusion coefficient of Bovine Serum Albumin at different ionic strength and determined the interaction parameter. The results indicate: the value of lambda is positive at low ionic strength and the interaction between proteins is repulsive; however, with increasing ionic strength the value of lambda becomes negative and the interaction is attractive, and when ionic strength is higher than 0.5 mol/L aggregation occurs. The dependence of the interaction on ionic strength is interpreted using Derjaguin-verwey-landau-overbeek (DLVO) theory for interactions of two hard spheres: with increasing ionic strength, the repulsive electrostatic interaction is screened and Van der Waals forces become dominant. According to the correlation of lambda with ionic strength, the protein parameters are regressed: the protein net charge Z(p) = -9. 0e, Hamaker constant A(H) = 2. 8k(B)T. Experimetns work indicate the technique of dynamic light scattering can be used effectively to study protein molecular interactions.