The Isoelectric Point ($pI$) is the specific pH at which an amino acid molecule carries no net electrical charge.

• At this pH, the amino acid exists primarily as a Zwitterion (a dipolar ion having both a positive $N{H}_3^{+}$ and a negative $CO{O}^{-}$ group).
• At $pH<pI$, it exists as a cation.
• At $pH>pI$, it exists as an anion.
• Amino acids show minimum solubility at their isoelectric point.