Isoelectric point
The isoelectric point (pI) of a protein is the pH where the proteins
has no net charge. The pI is calculated from the pKa values for
20 different amino acids. At a pH below the pI, the protein carries
a positive charge, whereas if the pH is above pI the proteins carry
a negative charge. In other words, pI is high for basic proteins and
low for acidic proteins. This information can be used in the
laboratory when running electrophoretic gels. Here the proteins can
be separated, based on their isoelectric point.