Question

Can you calculate the pI for the following peptide? Phe-Lys-Glu-Asp-Lys-Ser-Ala (note: there is one alpha carboxyl at the C-terminus and one alpha-amino group at the N- terminus and don't forget to take into account the ionizable side chain groups!)

Answer 1

answer : peptide chain pI is calulate by Finding the approximate pH where the net charge would be zero, and average the closest pKa values on either side of this value.

so in our case the pH range where the net charge is 0 for our peptide chain is 5 to 10

so we are taking pka value is less than pH 5 is Glu whose pka is 4.25 and the one whose pKa value is more than pH 10 but close to it 10.53 only one Lys value is taking

so average become (4.25 + 10.53) / 2 = 7.39