Gelation in cytochrome C concentrated solutions near the isoelectric point: the anion role

Proteins in concentrated solutions behave like colloidal system whose interaction potential can be finely tuned by changing temperature, pH, salt content and ion species. An anion-driven formation of protein clusters has been encountered eventually evolving in a structural arrested state as testified by both the appearance of a low Q peak in the small angle neutron scattering spectra and a strong increase in the relative viscosity of the samples. These phenomena, taken together, can be considered as the signature of a gelation process that specifically depends on the nature of anions, according to the Hofmeister series.