Novel Isoelectric Precipitation of Proteins in a Pressurized Carbon Dioxide-Water-Ethanol System

A novel isoelectric precipitation of proteins in a pressurized carbon dioxide-water-ethanol system was developed where carbon dioxide was used as a volatile acid. The pH-pressure curves of the system with the absence and presence of proteins were investigated. By introducing the pressurized carbon dioxide to a solution containing protein, the pH value in the solution was decreased to the isoelectric region of the model protein BSA. Addition of ethanol could lower the buffer capacity of the protein, which made the precipitation concentration of protein go beyond the limits in a system without ethanol and well exploited the application field of the technique. In addition, ethanol in solution played the role of aiding precipitation in the process. Another model protein, hen egg white lysozyme, was also studied but could not be precipitated in the above system. All of these phenomena prove that isoelectric precipitation is the key point in the pressurized carbon dioxide-water-ethanol system.