Quantitation of asparagine-101 deamidation from alpha-A crystallin during aging of the human lens

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Abstract
PURPOSE. To quantitate deamidation of asparagine-101 from the alpha-A crystallin protein of human lenses of different ages. METHODS. Alpha-A crystallin was purified from total proteins of human lenses of different ages, followed by tryptic digestion and resolution of the peptides, using reverse phase chromatography. Known amounts of synthetic peptide standards, corresponding to the amidated and deamidated forms of the expected tryptic peptide containing asparagine-101, were used to identify and quantitate the amount of deamidation. RESULTS. From 0–30 yrs of age, ~45% of asparagine-101 was deamidated, while only ~5% additional deamidation occurred during 30–68 yrs of age. CONCLUSIONS. In the normal human lens, most deamidation of asparagine-101 occurs during the first ~30 years of age, followed by a small additional amount of deamidation (~5%) during the next ~38 years, resulting in a maximum of ~50% deamidation during the lifetime of the individual.