ASPARTIC ACID RACEMIZATION IN RELATION TO HUMAN CATARACTOGENESIS

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Older citizens are fast becoming a greater percentage of the American population. With this trend, there is increasing concern over functional disabilities amongst this segment of the population. Visual disorders like cataract and macular degeneration, are the leading causes of blindness and constitute a major part of functional disabilities amongst older-persons. Age-related cataract is due, at least in part, to chemical modifications in lens proteins during the aging process. Amino acid racemization is one of the age-related changes that have been reported. It involves the stereoinversion of the L-form of a protein amino-acid, to its naturally uncommon D-form. This conformational change may lead to a structural change that may ultimately alter the function(s) of the modified protein. Past studies have documented increased D/L rations of specific aspartate residues of alpha-A crystallins from aged, cataractous human lenses and suggested a possible involvement of racemization in the pathogenesis of age-related cataract will aid in developing strategies for treatment, or at least, delaying the onset of this disabling disease. The long term objective of this project is to determine if the extent of aspartic acid racemization in human eye lens proteins, correlates with incidence of age-related cataract. The specific objectives are to utilize more reliable, sensitize methods, to quantitatively compare racemization of Asp-58, Asp-151 in alpha-A crystalline, and Asp-36, Asp-62 of alpha- B crystallins, isolated from cataractous and age-matched normal human lenses. This will be done by HPLC analysis of peptide fragments (containing the specified aspartate residues), derivatized with Marfey's reagent. Aspartic acid racemization will also be quantitated in water insoluble, urea-soluble protein fractions from cataractous and age- matched normal lenses, using a method that minimizes background racemization and estimates D-aspartic acid by oxidation with D-aspartate oxidase.