Zwitterions
- Neutral w/ counterbalancing +/- charges
- Can both accept and donate protons
- AA's are zwitterionic under physiologic conditions:
Isoelectric point (pI)
- No net charge
- For most AA: zwitterionic state = isoelectric point
- Charged amino acids (aspartic acid & arginine): isoelectric point may favor more acidic or more basic form of molecule
Zwitterions & the Isoelectric Point
- * Amino acids are zwitterions, meaning that these molecules can be neutral with counterbalancing positive and negative charges, because they can both accept and donate protons.
- Under physiological conditions, amino acids exist in their zwitterionic state with the amino group as NH3+ and the carboxylic acid as COO- (minus).
- Because of this distinct feature, each amino acid has an isoeletric point (pI) at which it has no net charge.
- For most amino acids, the isoelectric point is the zwitterionic state, but for charged amino acids, such as aspartic acid and arginine, the isoelectric point may favor a more acidic or more basic form of the molecule.