Age-dependent deamidation of chicken alpha A-crystallin.

The major posttranslational modification product of alpha A-crystallin from chicken eye lenses has one more negative charge than the corresponding primary gene product. These polypeptides were compared by peptide mapping after tryptic digestion and cyanogen bromide cleavage, and the charge difference could be located in a peptide, comprising residues 146-150 of the amino acid sequence of alpha A-crystallin. Subsequent enzymatic hydrolysis with aminopeptidase showed that asparagine at position 149 of the primary gene product is replaced by aspartic acid. Two-dimensional gel electrophoresis of total lens homogenates from chickens of different ages revealed an age-dependent increase of the deamidated alpha A-subunit.