The state of sulfhydryl groups in normal and cataractous human lens proteins. I. Nuclear region

Abstract

The level of water-insoluble proteins in the nuclear region of the human lens increases progressively with aging. Increases beyond the normal level occur with opacifications until more than 90% of the proteins in the nuclear region are water-insoluble in severe cataracts. The level of nuclear protein disulfide groups in cataract also is dramatically higher than that found in aged, normal lenses. More than 90% of the water-insoluble protein sulfhydryl groups are oxidized in advanced cataracts. Although water-soluble nuclear proteins of certain cataracts contain high levels of protein disulfide groups, the total amount of protein disulfides in the nuclear region that are soluble stay within the range of normal values. Part of the large increases from normal levels in acid-soluble sulfhydryl groups released by borohydride reduction of the insoluble fraction of advanced cataracts is probably due to an increased number of particular nondisulfide bonds susceptible to reductive cleavage. In spite of differences in the distribution of nuclear sulfhydryl and disulfide groups in aged, normal and cataractous lenses, the total amount of lens nuclear sulfhydryl plus disulfide groups remains reasonably constant.