The effect of urea on the aggregate state and elastase inhibitor activity of the water-insoluble fraction from bovine and human lens.

Preparations of alpha-crystallin from bovine and human lens exhibited elastase inhibitor activity with a specific activity of 100-250 U mg-1 protein. A washed water-insoluble fraction from bovine, human and cataractous lens nuclei, when solubilized by sonication, gave specific activities of 910, 950 and 1270 U mg-1, respectively. Disaggregation of these water-insoluble fractions in 8.0 M urea, with subsequent reaggregation by urea removal, resulted in a decrease in inhibitor activity. Agarose A-5m gel filtration chromatography after the urea treatment resolved a residual high molecular weight (HMW) fraction and a peak which eluted at the position of water soluble alpha-crystallin. Assays showed that the urea-induced 'alpha-crystallin' peaks from all three preparations had specific activities, equivalent to native alpha-crystallin, whereas the HMW fractions retained their original high specific activity. We conclude that the increased elastase inhibitor activity of the water-insoluble fraction is a property of the aggregate state of the component alpha-crystallin molecules, which is lost upon reaggregation to an 800-kDa alpha-crystallin. Amino acid analysis of the bovine water-insoluble fraction suggested a content of 85-90% alpha-crystallin and 10-15% beta H-crystallin, which was confirmed by SDS-PAGE.(ABSTRACT TRUNCATED AT 250 WORDS)