The effects of aging and cataract formation on the trypsin inhibitor activity of human lens.

Assays were carried out to determine the trypsin inhibitor activity present in the water-soluble and water-insoluble fractions of human lenses of various ages. Little change was seen in the inhibitor activity of the water-soluble protein fraction. When this fraction was chromatographed on an Agarose A-1.5 m column, however, the inhibitor activity was increasingly associated with the high molecular weight (HMW) protein fraction with age. A gradual increase in water-insoluble inhibitor was seen up to age 60, which correlated with the increase in protein in this fraction. After age 60, a marked increase in the water-soluble inhibitor activity was observed. In 80-90-yr old lenses, 1 mg of water-insoluble protein was able to inhibit 200 micrograms of crystallin trypsin by 50%. Similar assays on a collection of cortical and brunescent cataracts also showed very high levels of water-insoluble inhibitor activity. In most cases, these values were higher than those for the age-matched control lenses. Fractionation of the water-insoluble proteins showed that the bulk of the activity remained with the urea-insoluble fraction in cataractous lenses. A low molecular weight trypsin inhibitor was isolated from the water-soluble and water-insoluble fractions of human lenses. An age-dependent increase in this inhibitor was observed by activity measurements and electrophoretic analysis.