Phase Separation in Multicomponent Aqueous-Protein Solutions

published in Advance ACS Abstracts, December 1, 1994. 0022-3654/95/2099-0454$09.00/0 we present here the results of experimental and theoretical studies of a ternary solution constituted of the proteins yma (designated as protein A), a “high-Tc” protein, and yw (designated as protein B), a “low-Tc” protein, in aqueous solution. The solution pH was kept constant at 7.1 by a 100 mM phosphate buffer and the solution ionic strength was 240 mM. Both these proteins have the same effective volume S2p as their molecular weights are essentially the same and equal to 21 kDa. To facilitate the subsequent presentation it will be useful to introduce the fundamental quantities which we shall use to describe these solutions. Let NA, NE, and Nw be the total number of proteins A and B and water molecules in the solution. The effective volumes S2p and QW of protein and water molecules are chosen to subsume the effect of the ions so that the total volume V is given by V = N A R ~ + NBQP + NWSZw. In this work two sets of state variables naturally suggest themselves to describe the system. The f i s t set ( T , ~ A , ~ B ) are the temperature, the volume fractions of proteins A and B, and the volume fraction of water: