Glutamic acid (pK1 = 2.0, pK2 = 4.0, pK3 = 10.0) is dissolved in water. The isoelectric point (pI) of glutamic acid is

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The isoelectric point (pI) of an amino acid is the pH at which the molecule carries no net electric charge. For amino acids with three pKa values, like glutamic acid, which has two carboxyl groups and one amino group, the pI is calculated as the average of the pKa values of the two groups that lose protons at lower pH values (the carboxyl groups in this case). Thus, pI = (pK1 + pK2) / 2 = (2.0 + 4.0) / 2 = 3.0.

Glutamic Acid (PK1 = 2