AGE-DEPENDENT DEAMIDATION OF ALPHA-B-CRYSTALLIN

Bovine and human alphaB-crystallin undergo deamidation upon aging in t he lens. In bovine alphaB-crystallin, the specific site of deamidation has been identified by peptide mapping after tryptic digestion. Asn-1 46 was found to be subject to deamidation, whereas the only other aspa ragine residue, at position 78, is not affected. Asn-146 is flanked at the carboxylic side by a glycyl residue. Yet, the rate of in vivo dea midation is low. In vitro studies reveal that the deamidation is accom panied by significant racemization, indicating that the deamidation pr oceeds via formation of a succinimide intermediate.