The solubility of bovine lens crystallins

Apparent thermodynamic parameters for the process of solubilization of the five major classes of bovine lens crystallins have been determined by the polyethylene glycol solubility method. Although each purified crystallin fraction displays significant structural heterogeneity as analyzed by high performance liquid chromatography, they behave as homogeneous proteins by the criteria of solubility. Using experimentally determined values for the apparent enthalpy and entropy of solution and the effects of a variety of low molecular weight solutes on crystallin solubility, the five classes can be arranged in order of the polarity of their solid phase intermolecular contacts as follows: gamma, high molecular weight beta greater than low molecular weight beta greater than high molecular weight alpha greater than alpha. Since alpha-crystallin is the major component of the insoluble material in bovine cataract, we suggest that cataract formation may be related to the intrinsic solubility and polarity of the lens crystallins.