Intracellular degradation and deamidation of alpha-crystallin subunits.

The subunites AA2 and N2, present in alpha-crystallin from the nucleus of young and old bovine lenses, were isolated and characterized. It was found that AA2 is identical to a shorter A-chain and hence it was designated as A1-101. The subunit N2 turned out to be identical with a shorter B-chain and was designated as b 1/2-170. Characterization of the subunit N1, present only in alpha-crystallin from the cortex of old bovine lenses, suggested that his subunit is a modified B-chain, probably a deamidation product; it was designated as B0. Con relation to the age of the fiber cells in old bovine lenses with that in calf lenses revealed that the observed specific limited degradation of the subunits of alpha-crystallin increased with older age of the tissue. The deamidation process was found not to be related to the aging of the tissue. Eventually, a clear picture concerning the heterogeneity and fickleness of the alpha-crystallin subunit structure was obtained.