Zwitter Ion

A Zwitter Ion is formed when an amino acid is at it's isoelectric point. Most Zwitter ion's have no net charge, and therefore will not migrate in a charged field, it has both accepted a proton (H⁺) at it's N-terminus and lost a proton at it's C-terminus. However, it is possible for the R-group of an amino acid to interact in the same way, which can give the Zwitter ion 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.