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Isoelectric Point Calculator
Calculate the pH at which an amino acid carries no net electrical charge
Formula: $pI$ is the average of the two $pK_a$ values that bracket the neutral zwitterion state. For neutral amino acids, it's the average of $\alpha$-COOH and $\alpha$-NH₃⁺. For acidic/basic side chains, it incorporates the $pK_r$.
Amino Acid Properties
Calculation Results
⚠️ The isoelectric point ($pI$) is the exact pH where the molecule exists primarily as a zwitterion (net charge = 0). At pH values below the $pI$, the amino acid carries a net positive charge; above the $pI$, it carries a net negative charge.