The following amino acids will be in their zwitterionic forms at pH 4 EXCEPT Tryptophan Cysteine Glutamic acid Lysine . The Exceptions of Zwitterionic Forms of Amino Acids at pH 4

The Zwitterionic Amino acids at pH 4: Exceptions

The zwitterionic forms for the four amino acid – tryptophan and cysteine, glutamic, lysine – differ at pH 4. The zwitterionic forms for tryptophan (and cysteine) will be retained, while glutamic and lysine won’t. Cysteine and tryptophan have a pH of 4 neutral charges, so they can remain in their zwitterionic forms. The side chains of these amino acids contain two carboxylic group ends. These carboxylic group allow them to be neutral at pH 4 and keep them in their zwitterionic state (Kumar 2018).
However, glutamic and lysine cannot be left in their zwitterionic forms at pH 4. Glutamic acid is negatively charged at pH 4, due to its two carboxylic chains (Shih, et al. 2016). Similar to Glutamic acid, Lysine also has two carboxylic groups along its side chain. This makes it a negatively charged version at pH 4. (Mandal and al., 2002). This means that these amino acids can no longer be maintained in their zwitterionic forms at pH 4. Cont…