Intracellular Degradation and Deamidation of α‐Crystallin Subunits

Abstract

The subunits AA₂ and N₂, present in α‐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 A^1–101. The subunit N₂ turned out to be identical with a shorter B‐chain and‐was designated as B1/2⁻¹70. Characterization of the subunit N₁, present only in α‐crystallin from the cortex of old bovine lenses, suggested that this subunit is a modified B‐chain, probably a deamidation product; it was designated as Bo. Comparison of the appearance of degraded and deamidated chains in relation to the age of Uhc fiber cells in old bovine lenses with that in calf lenses revealed that the observed specific limited degradation of the subunits of α‐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 theα‐crystallin subunit structure was obtained.