| 초록 |
A variety of researches have studied the protein precipitation behavior by using various experimental techniques. These experimental results show the dependence on the factors, such as an ionic strength, a temperature, a salt concentration and solution pH. Several theoretical studies have been developed to predict the phase separation behavior of the protein solution. In these studies, most dependencies on the factors are discussed, however, the pH dependence yet has not been sufficiently studied. In this study, we present a molecular-thermodynamic frame work to describe the protein precipitation by inorganic salt. This equilibrium model represents the solution as a pseudo-one-component system containing only a continuous solvent and a globular protein molecule. Equation of state is the sum of a hard-sphere reference contribution and a perturbation. The reference term is derived based on the modified Chiew’s model to describe the pre-aggregating effect of protein, which can express the conformation change in pH. We also discuss protein-protein effective two-body potentials. The distribution and magnitude of charge on the surface of a protein charges significantly with pH. It changes the magnitudes of charge-charge repulsion, charge-dipole attraction, dipole-dipole attraction, and induced-dipole-induced-dipole attraction forces between protein pairs in solution. In the proposed model, pH and an ionic strength affect intermolecular potentials considerably. It predicts successfully the phase behaviors of protein solution with various pH. In the high salt concentration, pH dependence of the protein-protein interaction potential is not effective. In this case, the pH dependence is mainly affected by the conformation change, which can be expressed by.
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