Any charged or ionized group interacts with another through an electrostatic field. This may be calculated in a homogeneous medium by the classical equations of electrostatics which use a dielectric constant for the modulation of electrostatic effects. Solutions of proteins are very complicated subjectss for electrostatic calculations because of the heterogeneous dielectric constant at the interface of water and the protein. Unlike the energetics of other interactions in solution, the energetics of long-range electro static interactions may be simply and directly measured by protein engineering expreiments. If one of the charged group of is on the surface of the protein, it may frequently be removed by mutation, along with its field, with minimal disruption of the structure.

Charged Amino Acids