Controlled modulation of the phase separation and opacification temperature of purified bovine γIV-crystallin

Abstract

In the bovine lens the γIV-crystallin fraction is a principal determinant of the phase separation and opacification temperature, TC (Siezen et al, Proc. Natl. Acad. Sci. USA 82, 1985, 1701). We have now measured the effect on TC of purified γIV-crystallin solutions produced by a variety of reagents which affect protein-protein, protein-water and water-water interactions. Ionic strengths less than physiological increase TC dramatically, while higher ionic strength has very little effect. Calcium ion concentrations up to 8 mM produce no change in TC. Glycerol and acrylamide both depress TC linearly with reagent concentrations; TC depression of γIV-crystallin by these compounds is quantitatively the same as for whole lens. Sulfhydryl reducing agents such as glutathione and dithiothreitol lower TC, while hydrogen peroxide increases TC. Changes in opacification temperature of γIV-crystallin produced by oxidizing and reducing agents are time-dependent and highly non-linear with reagent concentration. Our results clearly show that bovine γIV-crystallin is an important target protein for various reagents which are known perturbants of the opacification temperature of whole lens. The relevance of these findings to human diabetic and senile cataract formation is discussed.