Discover the isoelectric point (pI) of your proteins and peptides instantly. This essential biological calculation helps predict the net charge of a molecule at a specific pH, vital for understanding its behavior in solutions and optimizing techniques like electrophoresis, chromatography, and protein purification. Simply input the pKa values of the ionizable groups to get an accurate pI determination.
Formula:
The isoelectric point (pI) is the pH at which a molecule carries no net electrical charge. For proteins, the pI is determined by the pKa values of its N-terminus, C-terminus, and all ionizable side chains. Our calculator finds the pH where the sum of all positive and negative charges on the protein equals zero, considering the protonation state of each group:
For Acidic Groups: Charge = -1 / (1 + 10(pKa - pH))
For Basic Groups: Charge = +1 / (1 + 10(pH - pKa))
The pI is the pH value where ∑Charges ≈ 0.