Salt-induced liquid-liquid phase separation of protein-surfactant complexes.

We report the cloud-point curve determination of lysozyme-sodium-doderyl-sulfate (SDS) complexes in solution. By varying the pH, salt concentration, and relative ratio of lysozyme to SDS, the phenomenon of clouding and liquid-liquid phase separation is investigated under different solution conditions. For the temperature, concentration, and pH ranges used in this study, the clouding phenomenon appears to be controlled by the electrostatic interaction between the lysozyme-SDS complexes. Any change in the solution condition that leads to a decrease in the charge on the lysozyme-SDS complexes results in an increase in cloud-point temperature. A generalized Flory-Huggins theory for polydisperse polymers is used to describe the cloud-point curve.