US Patent 8420789 Method for removing DNA contaminants from a protein-containing sample

A method is provided for purifying physiologically active proteins, especially antibodies, in order to remove impurities such as DNA contaminants and viruses with minimal loss of physiologically active proteins. The physiologically active protein is introduced into an aqueous solution of low conductivity at a pH of below the isoelectric point of the physiologically active protein to precipitate impurities as particles. The particles are removed, leaving a purified physiologically active protein.