Water binding capacity of mixtures of lens crystallins

The water binding capacity of mixtures of bovine lens crystallins were investigated by combined differential scanning calorimetry and thermogravimetric analysis techniques. Binary, ternary and quaternary mixtures of alpha, beta H, beta L, and lower molecular weight (LMW) crystallins were prepared in proportion of their natural abundance. The percentage of non-freezable water of the total water content was used as an index of the bound water in all these mixtures and it was obtained as a function of crystallin concentration. These experimental values were compared to theoretical values that were calculated from the water binding capacity of individual crystallins obtained previously [Bettelheim and Popdimitrova (1990) Exp. Eye Res. 50, 715-8]. The calculations were based on the assumption that the mixtures of crystallins have the same intermolecular interactions that exist in the individual crystallins. Thus, the difference between the experimental and theoretical curves is an indicator of the type of interactions that may exist among the different crystallins. In all mixtures the experimental bound water was higher than the theoretical, predicted value at physiological concentrations. The water binding capacity of the lyophilized thin lens sections, on the other hand, was lower than the theoretical, predicted value.