STRUCTURE IN PROTEIN SOLUTION CHANGING THE PH

In this paper we present a small-angle neutron scattering measurement on concentrated aqueous solutions of lysozyme. The ranges for the pH a nd for the ionic strength of the solutions are chosen in order to matc h the physiological values at which the enzymatic activity of the prot ein is at his maximum. The net charge has been determined by separate tritation experiment. The form factor and the structure factor were ex tracted from the experimental data. The structure factor is quantitati vely reproduced within a hard-sphere model with an attractive Yukawa-t ail potential. The importance in this kind of systems of the attractiv e interaction, even at far from zero net charge is highlighted.