The protonated amino group of an amino acid will lose a proton when the pH approaches 9.
The ionization state of amino acids depends on their pH. In an acidic medium the amino group of the amino acid is protonated while the carboxyl group is deprotonated, that is, they exist in dipolar form. As the pH increases, the carboxyl group will be the first one to give up a proton; the dipolar form will persist until the pH approaches 9 when the protonated amino acid will also lose a proton.
