If a protein solution is at a pH equal to this protein’s pI, the repulsive electrostatic forces between charges on the nearby protein molecules are minimized, resulting in the risk increase of the hydrophobic surface patches. These sites easily become aggregation hot spots. In most cases, antibodies have a pI above pH8.0 to fit our standard purification process. Antibodies with lower isoelectric points can affect the second step of purification process, with utilization of anion exchange chromatography and possibly increase the scope of the purification process. Successful samples with shifting the formulation pH away from the pI of a protein has shown to improve the protein’s stability. pI of an antibody can be modulated by protein engineering.

Normally the isoelectric point of a protein is calculated from its amount of charged residues in the primary amino acid sequence, utilizing EMBOSS pKa values.