In the late 19th century, Franz Hofmeister, professor of pharmacology at the University of Prague, and his colleagues studied the physiological effect of different salts and their concentrations on proteins in solutions. He found that the addition of salts to a protein solution affected not only its solubility but also other physico-chemical properties and stability. The effects depend on the type and concentration of the salt or ion. He classified salts according to their ability to stabilise proteins in solution, or more precisely, he classified ions according to their lyotropic properties, i.e. their ability to »salt-in« (chaotrope) or »salt-out« (cosmotrope) proteins from solution.
A typical representative of globular proteins is lysozyme. Lysozyme acts as a natural non-specific protector against bacteria and fungi. It has the ability to degrade and destabilize different varieties of cell wall polysaccharides. It is found in tears, saliva, egg white. It consists of 129 amino acids.
In this thesis we investigated the effect of different salts, cosmotropic and chaotropic ions on the solubility of globular proteins, specifically on HEWL. CaCl$_2$, Na$_2$CO$_3$, NaBr and NaF solutions were prepared and incubated with HEWL at different salt concentrations. The concentration ranges of the individual salts where HEWL precipitation occurs were then determined using UV-Vis spectroscopy. The dynamic light scattering method was used to measure the hydrodynamic radius of the resulting particles, the transmittance of the incubated solution and to determine the dependence of the first intensity peak and the size of the most common cluster on the concentration of added salts.
We showed the different influence of individual salts and ions on the precipitation of globular protein, with cosmotropic ions decreasing the solubility of the protein and facilitating its precipitation. On the other hand, chaotropic ions had the opposite effect.
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