PHASE-SEPARATION IN AQUEOUS-SOLUTIONS OF LENS GAMMA-CRYSTALLINS - SPECIAL ROLE OF GAMMA(S)

We have studied liquid-liquid phase separation in aqueous ternary solu tions of calf lens gamma-crystallin proteins, Specifically, we have ex amined two ternary systems containing gamma(s)-namely, gamma IVa with gamma(s) in water and gamma(LI) with gamma(s) in water, For each syste m, the phase-separation temperatures (T-ph(phi))(alpha) as a function of the overall protein volume fraction phi at various fixed compositio ns alpha (the ''cloud-point curves'') were measured, For the gamma(IVa ), gamma(s), and water ternary solution, a binodal curve composed of p airs of coexisting points, (phi(I), alpha(I)) and (phi(II), alpha(II)) , at a fixed temperature (20 degrees C) was also determined, We observ e that on the cloud-point curve the critical point is at a higher volu me fraction than the maximum phase-separation temperature point. We al so find that typically the difference in composition between the coexi sting phases is at least as significant as the difference in volume fr action. We show that the asymmetric shape of the cloud-point curve is a consequence of this significant composition difference, Our observat ion that the phase-separation temperature of the mixtures in the high volume fraction region is strongly suppressed suggests that gamma(s)-c rystallin may play an important role in maintaining the transparency o f the lens.