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Isoelectric Point (pI)

Isoelectric point (pI) is the pH where the net charge of a molecule is zero. At its pI, a molecule will not move in an electrical field because it does not have a charge.
An amphoteric molecule such as a protein in a pH below its pI will have a net positive charge (as shown below). Conversely, if the pH is above the pI, a protein will have a net negative charge.