Abstract
The salting-out effect of simple electrolytes on lysozyme has been studied by measuring the second virial coefficient B2of the osmotic pressure as a function of salt concentration, and for different salts. The aim of this work has been to find a microscopic counterpart of the empirical Hofmeister series for the efficiency of cations and anions in inducing protein crystallization. The experimental results show that, for large enough ionic strengths, B2scales linearly with the salt concentration. This trend is common to a number of different monovalent salts, however with efficiency strongly dependent on the specific anion. Conversely, changing the cation does not appreciably affect B2 . The significance of these findings for the investigation of protein interactions near crystallization is discussed.