Structural arrest in concentrated cytochrome C solutions: the effect of pH and salts

The effect of pH and different anions of sodium salts on concentrated solutions of cytochrome C protein have been investigated by means of small angle neutron scattering and viscosity measurements. The control and a fine tuning of protein-protein interactions leads to the formation of protein clusters that eventually evolve into a structural arrested state. The appearance of a low Q peak in the small angle neutron scattering intensity distributions is also accompanied by a strong increase in the relative viscosity. These phenomena taken together can be considered as the signature of the gelation process. This structural arrest is induced by salt addition and specifically depends on the nature of anions, according to the Hofmeister series.