Abstract

Below some critical temperature T_c aqueous solutions of hen-egg white lysozyme (HEWL) exhibit a phase-separation into two liquid phases with largely differing protein concentrations [1,2]. Similar observations were made with γ-crystalline [3], a bovine lens protein. In both cases, this phase separation is metastable since it occurs under crystallization conditions. The implication of this metastable separation for the determination of advantageous crystallization conditions has received little attention. Using static light scattering, we determined the transition temperature of the liquid-liquid phase separation vs. protein concentration, c_p, at salt concentrations typically used in crystallization experiments. We have also qualitatively investigated concanavalin A and apoferritin solutions for such phase transitions. Together with earlier solubility data, the light scattering results define the phase behavior of lysozyme solutions. These and the prior observations suggest a universal character of globular protein phase diagrams, and provide a rational underpinning for the empirically established narrow range of crystallization conditions.

© 1996 Optical Society of America