Given the following peptide ValMetSerGlyGluSerAspHis LysCysT

Given the following peptide Val-Met-Ser-Gly-Glu-Ser-Asp-His Lys-Cys-Tyr-Leu

a. What is the pi?
b. WhatisthenetchargeatpH7.0?

c. What is the net charge at pH 4.0?

Solution

a) The isoelectronic point or isoionic point is the pH at which the amino acid does not migrate in an electric field. This means it is the pH at which the amino acid is neutral, i.e. the zwitterion form is dominant.

Pi is the average of pKa1 and pKa2 or pKa3

b) zero

c) Negative charge