Aspartic acid racemization in heavy molecular weight crystallins and water-insoluble protein from normal human lenses and cataracts

High D/L aspartic acid ratios are observed in heavy molecular weight aggregates and in water-soluble protein extracted from whole lenses and nuclear and cortical regions. Purified α-, β-, and γ-crystallins have low D/L ratios. Fractionation of urea-solubilized material from the water-insoluble protein yields four molecular weight classes of proteins. Fractions representing crosslinked material or apparently degraded products have high D/L ratios. Racemization within lens proteins may contribute to formation of the water insoluble fraction seen in aging lenses and cataracts