A MODEL OF ATTRACTIVE INTERACTIONS TO ACCOUNT FOR FLUID-FLUID PHASE-SEPARATION OF PROTEIN SOLUTIONS

Concentrated gamma-crystallin and lysozyme solutions have been reporte d to undergo a fluid-fluid phase separation when cooled below a critic al temperature. This behavior is under control of the weak forces acti ng in solution between macromolecules. We have used small angle x-ray scattering at the synchrotron radiation facility LURE (Orsay, France) to analyze the interaction potentials. A model of attractive interacti ons which depends upon three parameters, protein diameter, potential d epth, and range, is able to account for both the x-ray structure facto rs measured at high temperature and for the low temperature phase sepa ration. Although van der Waals forces could be at the origin of the at tractive interaction potentials, other more specific effects also cont ribute to the protein phase diagrams. (C) 1996 American Institute of P hysics.