Zwitter Ion

A Zwitterion is formed when an amino acid is at it's isoelectric point. Most Zwitterion's have no net charge and therefore will not migrate in a charged field. This is because they accept a proton (H⁺) at their N-terminus and lose a proton at their C-terminus. However, it is possible for the R-group of an amino acid to interact in the same way, which can give the Zwitterion a net charge eg. if the R-group contains a carboxyl group (COOH) it may also donate the H⁺ from this group, creating a net charge of +1.