ANALYSIS OF OSMOTIC PRESSURE DATA FOR AQUEOUS PROTEIN SOLUTIONS VIA A ONE - COMPONENT MODEL 1

Yu. V. Kalyuzhnyi ^a;b , J. Rescic ^b and V. Vlachy ^{b a} Institude for Physics of Condensed Matter, Lviv, Ukraine ^b Faculty of Chemistry and Chemical Technology, University of Ljubljana, Askerceva 5, 1000 Ljubljana, Slovenia.

ABSTRACT

A modication of the one-component model of protein solutions is presented that accounts for the self-association of protein molecules in solution. In addition to the usual screened Coulomb interaction the protein molecules can form dimers, but no higher clusters are allowed. Essentially, we treat the solution as a mixture of hard spheres and hard dumb-bells characterized by some eective diameter. A simple variational approach is proposed to relate the eective diameter to the parameters of the solution under investigation, i.e. the real diameter of the protein, its charge and concentration. The new method is used to analyse the reported data for the osmotic pressure of three dierent proteins with various degrees of self-association. The method, which requires little numerical work, seems to be able to explain the osmotic pressure behaviour of protein solutions in terms of a single parameter, i.e. the fraction of dimers in solution.