The isoelectric point (pI) of a peptide is the pH at which the
peptide does not migrate in an electric field. Since the peptide is
zwitterionic, there are the same number of positive charges as
negative charges on the peptide population. The pI can be estimated
fairly accurately (within 0.1 or 0.2 pH units) from the pK values
of all the proton dissociable groups in the peptide. Using pK
values from the table at the right, estimate the pI value...